text stringlengths 1 1.11k | source dict |
|---|---|
javascript, optimization
function findClass(ip) {
if (ipInputArray.length === 4) {
if (!ip || ip < 0 || typeof ip === 'undefined') {
return "No Valid IP Entered";
}
if (ip < 128) {
return "Class A";
}
if (ip < 192) {
return "Class B";
}
if (ip < 224) {
return "Class C";
}
if (ip < 240) {
return "Class D";
}
if (ip < 256) {
return "Class E";
}
} else {
return "No Valid IP Entered";
}
}
for (var j = 0; j < submaskInputArray.length; j++) {
// finds the first octet not equal to 255
if (submaskInputArray[j] !== "255") {
index = j;
break;
}
} | {
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"url": null
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special-relativity, speed-of-light, kinematics, faster-than-light, relative-motion
However, the situation is different if he, now on ship A, measures the velocity of oncoming ship B. By classical addition of velocity, he will measure the velocity of ship B relative to his ship be $0.6c+0.6c=1.2c$, which is greater than the speed of light. This is probably what you are thinking about. However, if you read about Lorentz velocity transformation:
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/veltran.html
(Or you can google it yourself). The velocity of ship B, relative to ship A is $\frac{v_{A}+v_{B}}{1+\frac{v_{A}v_{B}}{c^2}}\approx0.882c$. | {
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"tags": "special-relativity, speed-of-light, kinematics, faster-than-light, relative-motion",
"url": null
} |
genetics, homework
Title: Question about using Mendelian inheritance to reverse-guess the parent genotype I would like some help with a question about Mendelian inheritance, based on the following information (I assume this is autosomal and not sex linked):
-- Start of information --
"As flatfish (Pleuronectiformes) develop, they lose their bilateral symmetry. One of their eyes migrates across the top of the head, so that both eyes end up adjacent on the same side of the head. As a result, the adult fish is able to lie flat on its side on the sea floor with both eyes facing up. In some species of flatfish the right eye migrates to the left side of the head (they are left-eyed); in other species the left eye migrates to the right side of the head (they
are right-eyed). | {
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special-relativity, time-dilation
I know that in general, if two frames $S$ and $S'$ are in relative uniform motion with respect to each other, and an observer in $S$ can see the clock of an observer $S'$ and the observer in $S'$ can see the clock of the observer $S$, then the observer in $S$ will see the clock of the observer in $S'$ run slower than his own, and vice versa. But I also know that $S'$ time is proper time, and so $t'\leq t$. This seems very strange to me. Observer $S$ sees his clock running faster, so intuitively, observer $S$ expects to measure less time for the event, but the time he measures for the light to return is no less than the time that observer $S'$ measures.
Am I understanding this correctly? I agree with your statements up through the claim that $t'<t$. That's all fine.
Here I think is the issue you're running into: | {
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The usual way to look for inflection points of f is to . Inflection Points: The inflection points of a function of an independent variable are related to the second derivative of the function. And where the concavity switches from up to down or down … I like thinking of a point of inflection not as a geometric feature of the graph, but as a moment when the acceleration changes. The Second Derivative Test cautions us that this may be the case since at f 00 (0) = 0 at x = 0. The Second Derivative Test cautions us that this may be the case since at f 00 (0) = 0 at x = 0. 2. x = 0 , but is it a max/or min. We observed that x = 0, and that there was neither a maximum nor minimum. For ##x=-1## to be an *horizontal* inflection point, the first derivative ##y'## in ##-1## must be zero; and this gives the first condition: ##a=\frac{2}{3}b##. (c) Use the second derivative test to locate the points of inflection, and compare your answers with part (b). There is a third possibility. Candidates for | {
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I'll show the resultant formulation for the degree 15 example.
The polynomial in question:
poly15 = (-282300416 - 64550400 # - 34426880 #^2 - 14185880 #^3 +
8564800 #^4 + 4231216 #^5 - 972800 #^6 - 367820 #^7 +
27360 #^8 + 2600 #^9 + 1680 #^10 + 100 #^11 - 240 #^12 +
40 #^13 + #^15) &[z];
Define monic polynomials of degree 3 and 5 with symbolic coefficients.
poly3[x_] := Array[a, 3, 0].x^Range[0, 2] + x^3
poly5[x_] := Array[b, 5, 0].x^Range[0, 4] + x^5
Here is the double-resultant way to get a polynomial whose roots are products of the roots of poly3 and poly5.
resxy = Resultant[Resultant[z - x*y, poly3[y], y], poly5[x], x];
Equate coefficients with this and the degree 15 polynomial. Since we can scale the two roots, force a constant term to be unity.
coeffs = CoefficientList[resxy - poly15, z] /. {a[0] -> 1}
Now solve:
solns=Solve[coeffs == 0] | {
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q-binomial coefficient '' is effectively dominant among research.... Operators and functions as you see, the command to display them in Latex mode we must use \binom as. To any whole number exponent text around it this uses the \choose operator instead! Possibility to insert operators and functions as you know them from mathematics is not possible for things. Similar to the one used for fractions they can be interpreted as number... A coffee also, the text around it parameters passed inside the second pair is the denominator outputs are.! Set of distinct items my channel: \frac { n {. In Latex mode we must use \binom fonction as follows: \frac { 1 } { k! Must use \binom fonction as follows: \frac { n } { k } \right ) }... Equation: math \frac { n - k } = \frac { }... Differs between \\dots and \\dotsc, with overleaf.com, the command \frac { }. Bootstrap and Spip by Nadir Soualem 's work circa 1640 also gives number... To insert operators and functions as you may have guessed, the | {
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are used as in. Of Comments on logarithmic functions just write an example exponential function will always be a positive number other [!, and graphs there are four basic properties in limits, which are used as formulas in evaluating limits! Evaluate an exponential function learn about the meaning of exponential functions occur frequently in sciences... These rules help us a lot in solving these type of equations, stretching, and of... Function, \ ( y=e^x\ ), is its own integral is equal to 3 to the x.... Have y is equal to 3 to the x power ( + ) = ( 2! Are variables or functions he learned that an experiment was conducted with one bacterium isn... Number in an exponential function ; next: the exponential function, \ y=e^x\. Research made on bacterial growth likely to consider the rule of exponents with logarithms given... A special category of functions that involve exponents that are variables or functions by the exponential function \! What is the inverse of another function we know | {
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quantum-mechanics, general-relativity, string-theory, higgs, large-hadron-collider
Title: What's next after Higgs Boson discovery?
Possible Duplicate:
Practical matter of the Higgs-Mechanism
As everybody knows that the Higgs Boson was discovered on July 4th,2012, I am so curious about it.
What are the possible outcome applications of Higgs Boson?
How Higgs Boson is related to Quantum Mechanics?
Does Higgs Boson fits in General Theory of Relativity?
Does Higgs Boson fits in String Theory? | {
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where $\tilde{w} \in \mathbb{R}$.
When $\tilde{w} = 0$, $\tilde{\mathbf{x}}$ is called ideal point and do not have the corresponding inhomogeneous coordinates.
## 3D Line Representation
Given two points $(\mathbf{p}, \mathbf{q})$ represented using inhomogeneous coordinates, on a 3D line, by vector algebra, we could represent any point $\mathbf{r}$ on the 3D line as a linear combination of the two points.
\begin{align} \mathbf{r} &= \mathbf{p} + \lambda (\mathbf{q} - \mathbf{p}) \\ &= (1 - \lambda)\mathbf{p} + \lambda \mathbf{q} \end{align}
Because any point on the 3D line can be represented using the expression above, the 3D line could also be represented using the exactly same expression.
Given one point $\mathbf{p}$ on a 3D line and its direction vector $\mathbf{d}$ represented using inhomogeneous coordinates, by vector algebra, we could represent any point $\mathbf{r}$ on the 3D line
\begin{align} \mathbf{r} &= \mathbf{p} + \lambda \mathbf{d} \\ \end{align} | {
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c#, unit-testing, graph
public Node(string name)
{
if (String.IsNullOrWhiteSpace(name)) throw new ArgumentNullException(nameof(name));
Name = name;
Links = new Collection<Link>();
}
public override bool Equals(object obj)
{
Node node = obj as Node;
if (node == null) return false;
return Name.Equals(node.Name);
}
public override int GetHashCode()
{
return Name.GetHashCode();
}
/// <summary>
/// Creates links betwen two nodes
/// </summary>
/// <param name="a">First node</param>
/// <param name="b">Second node</param>
/// <param name="distance">Distance between nodes</param>
/// <remarks>There is no order in the nodes</remarks>
public static void Join(Node a, Node b, int distance)
{
if (a == null) throw new ArgumentNullException("a");
if (b == null) throw new ArgumentNullException("b"); | {
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ros-kinetic
Original comments
Comment by k's on 2019-10-09:
thank you for your help.
Do I need to reinstall ROS to do apt?
Comment by gvdhoorn on 2019-10-10:\
Do I need to reinstall ROS to do apt?
No, I don't believe so.
Are you seeing any messages from apt that make you think so?
Comment by k's on 2019-10-11:
I see.
No, not yet. | {
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fluid-dynamics, conservation-laws, flow
Shouldn't that be against the equation of continuity which says that the flow rate must be constant. You are looking at the volume only in time, but you are forgetting how volume is calculated in the first place:
$$dV = A \cdot ds$$
where $A$ is the cross-section area and $ds$ is the infinitesimally small tube length for which you are calculating the infinitesimally small volume:
$$ds = v \cdot dt \tag 1$$
where $v$ is the fluid velocity and $dt$ is the infinitesimally small time. The Eq. (1) is key to understanding where your reasoning is wrong - for the same time $dt$ the fluid covers longer distance through smaller cross-section area, which we prove via mass flow.
The infinitesimally small mass flowing into the tube across $A$ in time $dt$ is:
$$dm = \rho \cdot dV = \rho \cdot A \cdot v \cdot dt$$
where $\rho$ is the fluid density which is constant for incompressible fluids.
Since the mass is not stored in the system, for any two points in the tube we have | {
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is defined as a number sequence having the particularity that the first two numbers are 0 and 1, and that each subsequent number is obtained by the sum of the previous two terms. Fibonacci Sequence is popularized in Europe by Leonardo of Pisa, famously known as "Leonardo Fibonacci". Scope of the formula in C. Binet 's formula, the recurrence is, and then using the recursive.! Liber Abaci is so named because it was derived by mathematician Jacques Philippe Marie Binet, though was. N = n th term of the Golden MEAN the Binet 's formula in C. Binet 's formula C.... Numbers arises all over mathematics and also in nature he made significant contributions to number theory and the sequence... The name of Golden Ratio and the Golden MEAN could start with 0 or.. Of 1 has a polar equation similar to that of other logarithmic SPIRALS you just need practice... Task to research on it comes out as a whole number, exactly equal the... Are generated by setting F 0 = 0, F 1 = 1 and. On Pinterest was | {
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php, array, random
This isn't too bad, really, just remove the function-call, and you're good, and perhaps shorten the if-else to a ternary or a single if-statement. you could argue that assigning the random number to a variable isn't really necessairy. You're using $i as an array-key, so you could assign the value to the array directly, and check the value there
for($i=0;$i<10;$i++)
{
$products[$i] = mt_rand(1,10);//$i is the key, so we don't need any other vars
$products[$i] .= 'car '.($products[$i] > 1 ? 's' : '');
}
//without ternary:
for($i=0;$i<10;$i++)
{
$products[$i] = mt_rand(1,10).' car';//just concat car already
if ($products[$i] > 1)
{//comparing to int will cast $products[$i] to int
//since the string starts with an int, it'll compare that int
//'4 car' > 1 ~~> 4 > 1 ~~> true ==> '4 car' .= s ===> 4 cars
$products[$i] .= 's';
}
}
Then, the output loop:
//Outputs the final array.
foreach ($products as $current){
echo $current."<br />";
} | {
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ros, python, homebrew, osx, transform
My python version is 2.7.6 from homebrew. I don't even know how to start debugging this. Any help is greatly appreciated.
Edit:
This seems to be caused by faulty cmake find_package(PythonLibs), which in turn caused by _tf.so to be linked against apple's python, while I'm using brewed python. I opened this issue: https://github.com/mxcl/homebrew/issues/25118.
I guess the question that remains is if anybody else has the same issue. For me it is not isolated to tf, but all python modules that are built with find_package(PythonLibs) and link against the found python libs.
Edit2:
[moved to new question]
Edit3:
When used to be Edit2 is now a new question as suggested. Thanks.
http://answers.ros.org/question/110671/recommended-python-version-on-os-x-with-homebrew/
Originally posted by demmeln on ROS Answers with karma: 4306 on 2013-12-09
Post score: 4 | {
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proteins, digestive-system
Heat cause denaturation of proteins. Once denatured, proteins are more susceptible to the enzymatic digestion. Thus, more nutrients are absorbed. There are also macroscopic phenomena in play, for example, a cooked piece of meat is more tender than the raw one, making mastication easier and less energy consuming.
The fact that you may feel your stomach upset because of raw food is probably due to the fact that you were never used to it. Your intestinal flora has been selected during the year to deal with the food you usually eat, any "new" food may cause the same symptoms. Humans that eat regularly raw food will not feel the same way. | {
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botany, terminology, nomenclature
Title: "Higher plants" or "vascular plants"? What is the difference — if any — between "higher plants" and "vascular plants"?
On Wikipedia, "higher plants" redirects to "vascular plants", which seems like an indication that both terms are essentially the same.
Is one of the terms preferred over the other?
Is one of the terms preferred over the other?
Absolutely: "vascular plants" is the preferred one. "Higher plants" should be avoided. Here is a long explanation:
The Great Chain of Being
This term "higher plants", together with the term "higher animals", is just a remnant of a completely wrong concept that has (or shouldn't have) no place in the world after 1859: the Great Chain of Being, or scala naturae in Latin.
This is the typical medieval representation of the scala naturae:
The Latin text on the ladder says: stone, fire, plant, beast, man, heaven, angel, god.
And here a more "modern" version of it (but equally wrong): | {
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ros
Title: Why "subs_.push_back" in listener_with_userdata.cpp
In the tutorial of listener, there is an example for listener_with_userdata, why we use push_back to initialise the three different callback functions.
class Listener
{
public:
ros::NodeHandle node_handle_;
ros::V_Subscriber subs_;
Listener(const ros::NodeHandle& node_handle)
: node_handle_(node_handle)
{
}
void init()
{
subs_.push_back(node_handle_.subscribe<std_msgs::String>("chatter", 1000, boost::bind(&Listener::chatterCallback, this, _1, "User 1")));
subs_.push_back(node_handle_.subscribe<std_msgs::String>("chatter", 1000, boost::bind(&Listener::chatterCallback, this, _1, "User 2")));
subs_.push_back(node_handle_.subscribe<std_msgs::String>("chatter", 1000, boost::bind(&Listener::chatterCallback, this, _1, "User 3")));
} | {
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climate-change
Title: Is 2015's record average temperature evidence that we are now experiencing runaway climate change? 2015 had the highest global temperatures on record, as discussed in this question, beating the last record ... in 2014.
Are we now in a runaway climate change regime, where zero further human impact on the environment will not prevent change to the equilibrium state of the Earth's atmosphere? Runaway climate change is, given our current state of knowledge, only something that could be confirmed in historic context - in the rear-view mirror. Inconveniently, there's likely to be a much-diminished version of human civilisation around to observe it, if and when it does happen.
In other words, it's too early to tell if we've passed a catastrophic tipping point. | {
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javascript, jquery, to-do-list
$("#add").click(function(){ todo_item.addItem(); });
$(".star").click(function(){ todo_item.toggleStar(); });
})
function checkLocalStorageBrowserSupport(){
if(!window.localStorage) {
// notify user
$("#info").text("Your browser does not support the HTML5 feature 'localStorage'. Please use an updated browser for this application to work.");
// stop
return false;
} else
return true;
}
function checkLocalStorageExistingData(){
if(localStorage.getItem('todo_items')){
var todo_items_json = localStorage.getItem('todo_items');
var todo_items = todo_items_json ? JSON.parse(todo_items_json) : [];
todo_items.forEach(function(item){
var item_content = item[0];
var star_check = item[1];
var checked = "";
if(star_check) checked = "checked"; | {
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There may be weaker conditions that would also suffice, but these tend to work in 99% of cases.
Elaborating on request: the usual statement of Fubini's theorem goes something like this:
Let $(X,\mathcal{F}, \mu),(Y,\mathcal{G}, \nu)$ be $\sigma$-finite measure spaces, and let $g : X \times Y \to \mathbb{R}$ be measurable with respect to the product $\sigma$-algebra $\mathcal{F} \otimes \mathcal{G}$. Suppose that $\int_X \int_Y |g(x,y)| \nu(dy) \mu(dx)$ is finite. (Note: By Tonelli's theorem, this happens if and only if $\int_Y \int_X |g(x,y)|\mu(dx)\nu(dy)$ is finite, since both iterated integrals are equal.) Then $$\int_X \int_Y g(x,y) \nu(dy)\mu(dx) = \int_Y \int_X g(x,y) \mu(dx) \nu(dy).$$ | {
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quantum-mechanics, general-relativity
String theory is the only known reconciliation of general relativity and quantum mechanics and chances are high that this status won't ever change.
There's of course no contradiction between "appropriately reduced in reach" general relativity and "appropriately tamed" quantum mechanics – after all, to a certain extent, both of these frameworks have been established so there has to exist a more accurate theory that agrees with all the established insights. | {
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thermodynamics, differential-geometry, temperature, calculus, equilibrium
$C_1=F_{AC}(A_1,...,A_n,C_2,...,C_n)\tag{3}$
$C_1=F_{BC}(B_1,...,B_n,C_2,...,C_n)\tag{4}$
Thus if C is separately in equilibrium with A and B, we must have
$F_{AC}(A_1,...,A_n,C_2,...,C_n)=F_{BC}(B_1,...,B_n,C_2,...,C_n)\tag{5}$
However, according to the zeroth law there is also equilibrium between
A and B, implying the constraint
$f_{AB}(A_1,...,A_n,B_1,...,B_n)=0\tag{6}$
We can select any set of parameters ${\{A,B}\}$ that satisfy the above equation, and
substitute them in $Eq. 5$. The resulting equality must hold quite independently of any set of variables ${\{C}\}$ in this equation. We can then change these
parameters, moving along the manifold constrained by $Eq.6$, and $Eq.5$
will remain valid irrespective of the state of $C$. Therefore, it must be possible
to simplify $Eq.5$ by canceling the coordinates of $C$. Alternatively, we can
select any fixed set of parameters $C$, and ignore them henceforth, reducing the
condition $Eq.6$ for equilibrium of $A$ and $B$ to | {
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"url": null
} |
sensors, microcontroller, design, electronics, laser
I have to be exactly accurate regarding the laser diode's position,
it has to be on the center of the holes, right below the z-axis.
This should be easy if I'm just going to place 4 or 5. But I'm not.
According to my estimations, I'm going to have to use 300-700 laser
diodes, depending on if I'm planning on putting the lasers only on
the opponent's side or on the entire board. It would definitely be
costly. Imagine 300...
This isn't really a huge problem, more like a hassle. Wiring 300 of
these. Forget the pcbs, the project area is just to large. | {
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"url": null
} |
c, game, memory-management, console, hangman
if (!word) {
return NULL;
}
for (int i = 0; i < length * 2; i++) {
word[i] = ' ';
}
for (int i = 0; i <= length - 1; i++) {
if (mysteryWord[i] == ' ') {
word[i * 2] = ' ';
}
else if (isalpha(mysteryWord[i]) != 0) {
word[i * 2] = '_';
} else {
word[i * 2] = mysteryWord[i];
}
}
return word;
}
/*
* contains takes in the mysteryWord array,its length and the user input
* it returns how many times the input occurs in the array
*
*/
int contains(char mysteryWord[], char input, int arrayLength) {
int a = 0;
if(isalpha(input)==0 && input != '_')
{
return 2;
}
char flipInput;
;
if (isupper(input) != 0) {
flipInput = tolower(input);
} else {
flipInput = toupper(input);
} | {
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"tags": "c, game, memory-management, console, hangman",
"url": null
} |
javascript, api
A style declaration that uses the ID but comes after your styles.
A style declaration that uses an ID and another attribute.
An inline style or style set using JavaScript.
Any selector, but with properties using !important.
You don't want your CSS specificity to be very high. Otherwise, you'll be eating up this list up to the last item until you can't style the element anymore.
With both issues, consider using the BEM naming scheme. In a gist, it solves both problems by 1) using classes and 2) classes have very low specificity. This will give you collision-free naming as well as easy overriding of styles. | {
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Calculate the volume of a pyramid. For engine's, this would be: Swept Volume = 3. They next must know the height of the cylinder. Volume of Hollow Cylinder. Volume of a Cylinder. 5) 2 x 3 = 21. Hence mathematicians usually use terms such as dz approaching zero. VOlume of lateral Cylinder V = B * h Where, B= Base area of the Oblique Cylinder h = height of the Cylinder, measured, perpendicular ot the base. Example 1 : Find the volume of the cylinder given below. , you can just multiply the two together to get the volume of the cylinder. Indeed, representing a cell as an idealized sphere of radius r, the volume and surface area are, respectively, V = 4/3 π r 3; SA = 4 π r 2. The radius of the circle is represented by. The volume of a cylinder as well as the dimensions that are related to it can be calculated by merely inputting those values that are already known to the user. A 5-m-wide cloth is used to make a conical tent of base diameter 14 m and height 24 m. - I'm creating a cylinder | {
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"openwebmath_score": 0.8166462779045105,
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"url": "http://campercom.it/sjlv/volume-of-a-circle-cylinder.html"
} |
Moving from B to C, we will move 5 times as much.
. . $\begin{array}{ccccc}x &=& 2 + 5(3.2) &=& 18 \\ y &=& 6 + 5(1.6) &=& 14\end{array}\quad\Rightarrow\quad C(18,14)$
Moving from B to A, we move 6 right and 4 down.
Moving from C to D, we will move the same.
. . $\begin{array}{ccccc}x &=& 18 + 6 &=& 24 \\y &=& 14 - 4 &=& 10\end{array} \quad\Rightarrow\quad D(24,10)$ | {
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"url": "http://mathhelpforum.com/pre-calculus/41677-questions-about-binomial-expansions-coordinate-geometry.html"
} |
quantum-spin, hamiltonian, notation, spin-models
\begin{equation}
s_\sigma(i) = I\otimes I\otimes\cdots I\otimes \underbrace{s_\sigma}_{i\text{th position}}\otimes I\cdots \otimes I
\end{equation}
which makes $s_\sigma(i)$ a $(2s+1)^N$ dimensional matrix. | {
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c++, strings, pointers
Title: C++ string_id, a O(1)-copyable and O(1)-comparable non-modifiable string class I was trying to find any way of developing a "string_id", a non-modifiable string holder that is O(1)-copyable and O(1)-comparable to be used as an id. The "creator" of the string_id is who knows the meaning of each "string_id". So, if two different entites creates two ids, that string_id identifiers represent different ids even if they strings representations are equal. Each newly and non-copied object creates a different id.
So, two string_ids refers to the same string iif they are in the same copy-hierarchy (a tree of copied objects), and not because their values compares equal. | {
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c++, linked-list
Same simplification
void push_back(T const& val) // insert element at back
{
tail = new Node(val, tail, nullptr);
if (head == nullptr) {
head = tail;
}
}
end() should be one past the end of the container.
it end() const // get end iterator
{
return it(tail);
}
If you do this the standard algorithms are going to miss the last element in the list.
I would do:
it end() const {return it{nullptr};} | {
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ros, serial, catkin, compilation, ros-indigo
Now, I really don't know why the compiler is not able to solve that reference. I tried unistalling and reinstalling serial, but nothing changed. Any suggestion?
--- edit ---
The CMakeLists.txt file I'm using is exactly the same reported in this git repository https://github.com/MirkoFerrati/irobotcreate2ros/blob/master/CMakeLists.txt
Thanks
Originally posted by McKracken82 on ROS Answers with karma: 73 on 2016-03-18
Post score: 0 | {
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In my book it also says that:
h(064212848) = 037149212 mod 111 = 14 , but I don't see how this can be correct. I mean, I am sure the book is correct, I just don't understand why hehe. I really hope someone can help me. Thank you!
What do you mean by h(064212848)?
6. ## Re: Questions about modular arithmetic
Originally Posted by Nora314
I am a little bit confused about modular arithmetic. I don't quite understand what it really means when one number is logically equivalent to another. For example in my book it says:
7 ≡ 2 (mod 5)
Drop the concept "one number is logically equivalent to another"
That has no place here if you are just starting to learn this topic.
Here the symbol $\equiv$ is use mathematically to mean equivalent class.
To say that integers $m\equiv n\mod k$ means that $m~\&~n$ have the same remainder when divided by $k$.
Thus $13\equiv 19\mod 6$ but $16\not\equiv 23\mod 5~.$
7. ## Re: Questions about modular arithmetic | {
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"url": "http://mathhelpforum.com/discrete-math/204733-questions-about-modular-arithmetic.html"
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### Show Tags
03 Aug 2010, 01:20
17
5
bibha wrote:
A coin made of alloy of aluminum and silver measures 2 x 15 mm (it is 2 mm thick and its diameter is 15 mm). If the weight of the coin is 30 grams and the volume of aluminum in the alloy equals that of silver, what will be the weight of a coin measuring 1 x 30 mm made of pure aluminum if silver is twice as heavy as aluminum?
36 grams
40 grams
42 grams
48 grams
Coin is in the shape of a cylinder.
Coin 1
Volume = pi* $$7.5^2$$*2 = 112.5pi cubic mm
Total coin weight(including both Aluminium and Silver)= 30g but Silver is twice as heavy as aluminium.
So weight of silver = 20g and weight of aluminium =10g
Volume of aluminium = Volume of silver
volume of aluminium = volume of silver = 112.5pi/2 = 56.25pi
So 56.25pi cubic mm of aluminium weighs 10g
Coin 2 | {
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"openwebmath_score": 0.6118152141571045,
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"url": "https://gmatclub.com/forum/a-coin-made-of-alloy-of-aluminum-and-silver-measures-2-x-15-mm-it-is-98446.html"
} |
symmetry, atmospheric-science, crystals, ice
I am looking for answers based on credible scientific sources.
Update
As the diagram given in the @JohnDumancic answer below demonstrates, snow crystals grow in the form of plates at temperatures from 0 to $-3^\circ$C or below $-10^\circ$. The question is thus essentially reduced to the typical conditions (temperature and water vapour saturation) that exist in the snow clouds. | {
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"url": null
} |
javascript, object-oriented, node.js, ecmascript-6, promise
}
scanFolder(callback) {
scanDirectory(this.filePath)
.then(files => {
this.findOldPdfs(this.filePath, files, (err, info) => {
if (err) return callback(err, null);
return callback(null, info);
});
}).catch(err => {
callback(err, null);
});
}
findOldPdfs(filePath, pdfs, callback) {
var pdfDates = getPdfCreateDates(filePath, pdfs);
Promise.all(pdfDates)
.then(pdfs => {
this.deletePdfs(pdfs, (err, info) => {
if (err) return callback(err, null);
return callback(null, info);
});
})
.catch(err => {
callback(err, null);
});
}
deletePdfs(pdfObjects, callback) {
var pdfsToDelete = getPdfsToDelete(pdfObjects, this.currentDate, this.maxPdfAge);
Promise.all(pdfsToDelete) | {
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"openwebmath_score": null,
"tags": "javascript, object-oriented, node.js, ecmascript-6, promise",
"url": null
} |
javascript, game, ecmascript-6, vue.js
Object.assign(enemyDeck.cards[cardID], {
used: false,
selected: false,
locked: false
});
});
};
const DarkerColors = {
"#DFB720": "#BF5700",
"#B0C4DE": "#90A4CE",
"#C0C0C0": "#A0A0A0",
"#DD00DD": "#BB00BB",
"#DF5F30": "#BF3F10"
},
LighterColors = {
"#DFB720": "#FFD940",
"#B0C4DE": "#D0E4FE",
"#C0C0C0": "#E0E0E0",
"#DD00DD": "#FD00FD ",
"#DF5F30": "#FF7F50"
}
var playerDeck = new Deck(false, null, playerWeights),
enemyDeck = new Deck(false, null, enemyWeights),
enemyHand = new Deck(true, new ManaManager(enemyDeck), enemyWeights),
playerHand = new Deck(true, new ManaManager(playerDeck), playerWeights),
playerManaManager = playerHand.manaManager,
enemyManaManager = enemyHand.manaManager;
Object.assign(enemyDeck, {
manaManager: enemyManaManager, | {
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c++, c++11, networking
char *dataTail(){
return & buffer_[tail_];
}
size_t size() const{
return tail_ - head_;
}
size_t capacity() const{
return CAPACITY - tail_;
}
// ==================================
bool push(const char *p){
return p ? push(strlen(p), p) : false;
}
bool push(size_t const len, const void *ptr = nullptr){
if (len == 0)
return false;
if (capacity() < len)
return false;
if (ptr)
memmove(&buffer_[tail_], ptr, len);
tail_ = (size_type) (tail_ + len);
return true;
}
bool pop(size_t const len){
if (len == 0)
return false;
auto const available = size();
if (available < len)
return false;
if (available == len){
clear();
return true;
}
head_ = (size_type) (head_ + len);
return true;
} | {
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is used in applications involving circular convolution and Discrete Fourier Transform (DFT)[2]. matlab code for circular convolution By Unknown at Wednesday, January 02, 2013 circular convolution , MATLAB 4 comments The circular convolution, also known as cyclic convolution, of two aperiodic functions occurs when one of them is convolved in the normal way with a periodic summation of the other function. This is generally much faster than convolve for large arrays (n > ~500), but can be slower when only a few output. • Examples 2. transform DFT sequences. 3 Circular convolution • Finite length signals (N • In this way, the linear convolution between two sequences having a different length (filtering) can be computed by the DFT (which rests on the circular convolution) 2D Discrete Fourier Transform • Fourier transform of a 2D signal defined over a discrete finite 2D grid. , given a linear system determine if it is causal. By the end of Ch. Convolution is often interpreted as a filter, | {
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"url": "http://coopruah.it/baax/linear-convolution-using-dft-examples.html"
} |
python, beginner, python-3.x
An infinite loop, a misused exception handling,
an incorrect error handling, and recursive calls...
This is confusing and more complicated than it needs to be.
You can replace the recursive calls with continue.
Exception handling for converting the input to integer is appropriate, because there is no better way. It is not appropriate for validating the input is within range, because a better way exists using conditionals.
Also, it's not enough to check that the index is less than the length of the list, you also need to check that it's 0 or greater.
UnboundLocalError is thrown when trying to access a variable that hasn't been assigned. That's not an exception to catch, it indicates a problem in the logic that needs to be fixed.
Here's one way to address these issues:
while True:
try:
to_remove = int(input('To remove a selection enter the number of the selection you want removed here. >>> '))
except ValueError:
print('Enter a number.')
continue | {
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Thanks for the link ! Many other nice articles
Too bad the article never touch any details about the fastest method, except O(n log(n))
If anyone want to see real code for other mentioned method, I have some code examples.
Note: MAPM number does based-100, and based-10000 for FFT calculations.
Karatsuba’s method : mapm_fmul.c
Fast Fourier Transform: mapm_fft.c
04-15-2019, 07:50 PM
Post: #3
Valentin Albillo Senior Member Posts: 388 Joined: Feb 2015
RE: MCODE: Fastest way to multiply
.
Hi, PeterP, long time no see:
(04-15-2019 03:58 PM)PeterP Wrote: For the MCODE gurus here, it seems one might be able to 'update' the OS routine for multiplication when doing large multiplications. | {
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recursion, scheme
You can use a similar approach for solving your problem iteratively:
(define (mX n m)
(let loop ((m m)
(product 0))
(if (zero? m)
product
(loop (- m 1) (+ product n)))))
Notice that we are not setting variables here. We are doing a tail recursion into loop, which is passed the new m and product values as arguments. | {
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visible-light, refraction, dispersion
If you have a material that has a positive slope in the range of frequencies of interest, your relationship holds - this is the "normal dispersion" range. But in general it doesn't (because of the "anomalous dispersion" that occurs around regions of resonance).
In general, the refractive index follows an equation of the form
$$\frac{n^2(\omega)-1}{n^2(\omega)+2} = \frac{Nq_e^2}{3\epsilon_0 m_e} \sum_j \frac{F_j}{\omega_{0j}^2 - \omega^2+i\gamma_j \omega}$$ | {
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"openwebmath_score": null,
"tags": "visible-light, refraction, dispersion",
"url": null
} |
automata, nondeterminism
Title: Is this language $X = \{x:xxx\in L\}$ regular? I came across this question in my Theory of Computation class recently:
Consider a regular language $L$, and define $X = \{x:xxx\in L\}$. Is this language regular?
I believe that it is regular, and that the procedure required to construct an NFA for it is not particularly different from constructing one for $W=\{x:xx\in L\}$ (at the very least, the one I will now attempt to do). | {
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"tags": "automata, nondeterminism",
"url": null
} |
c#, .net, generics, stack, queue
public T Current
{
get
{
if (_index == -2) throw new InvalidOperationException("EnumNotStarted");
if (_index == -1) throw new InvalidOperationException("EnumEnded");
return currentElement;
}
}
Object System.Collections.IEnumerator.Current
{
get
{
if (_index == -2) throw new InvalidOperationException("EnumNotStarted");
if (_index == -1) throw new InvalidOperationException("EnumEnded");
return currentElement;
}
}
void System.Collections.IEnumerator.Reset()
{
if (_version != _stack._version) throw new InvalidOperationException("EnumFailedVersion");
_index = -2;
currentElement = default(T);
}
}
} | {
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"id": 34670,
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"openwebmath_score": null,
"tags": "c#, .net, generics, stack, queue",
"url": null
} |
nielsen-and-chuang, stabilizer-code
Given $n-k$ generators, from their representation in terms of bit-vectors, it is easy to see that we can always find some $k$ additional independent generators. However, how can we be sure that we can always find $k$ additional commuting generators? The way that I tend to think about it is to write out the $(n-k)\times 2n$ binary matrices specifying the generators. The first $n$ bits of each row are the locations of Pauli $X$ matrices, while the second $n$ are the locations of the Pauli $Z$ matrices.
$$
G=\left(\begin{array}{c|c} G_x & G_z \end{array}\right)
$$
Now, imagine we introduce a new stabilizer $g=(x|z)$. It is linearly independent if $G\cdot G^t\equiv 0\text{ mod }2$. Also, it commutes if $G\cdot (z|x)^T\equiv 0\text{ mod }2$. In other words, we're looking for a vector that satisfies
$$
\left(\begin{array}{c|c} G_x & G_z \\ G_z & G_x \end{array}\right)\cdot g\equiv 0\text{ mod }2.
$$
Hence, we simply seek a member of the Null Space, modulo 2, of the big matrix. | {
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"url": null
} |
javascript, jquery, css
} else {
$('#black, #igna').slideUp("fast", function() {
$('#fatal').animate({ left: 'hide' }, 300);
});
}
$('#igna-1-div').fadeIn('500');
$('#igna-1-credits').fadeIn('3000');
$('#dust-div, #black-div, #fatal-div, #hurt-div, #youth-div, #black-credits, #igna-2-div, #igna-2-credits, #fatal-credits').fadeOut('100');
});
$("#igna-2 a").click(function(){
if ( $('#igna-1').css('display') != 'none' ) {
$('#igna-1').slideToggle("fast", function() {
$('#igna-2').animate({ left: 'hide' }, 300, function() {
$('#black, #igna').slideUp("fast", function() {
$('#fatal').animate({ left: 'hide' }, 300);
});
});
});
} else if ( $('#igna-1').css('display') == 'none' ) {
$('#black, #igna').slideUp("fast", function() {
$('#fatal').animate({ left: 'hide' }, 300);
}); | {
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} |
agriculture
When new varieties of rice are developed, test plots are planted in various locations and the yield per area of land, typical tonnes per hectare, are ascertained. Once this has been done for a number of test plots and for a number of growing seasons, average numbers of tonnes per hectare can then be applied to larger/national plantings.
Combine this with data regarding the number of people that need to be fed and the determined average of the amount of rice each person needs it is possible to determine the sufficiency of a rice production. | {
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onto the first cylinder (Fig. The moment of inertia is intimately linked to the definition of angular moment of a rigid body: For a rigid body rotating with angular velocity about a fixed axis, the angular momentum is. The can of jellied cranberry sauce is a solid cylinder. Centripetal acceleration at point P: Tangential acceleration at point P: The distances of the masses to the rotation axis is same. The equation specifying the proportionality is a rotational version of Newton’s second law: ˝ = I (1). Moment of Inertia--Rod The moment of inertia of a thin rod of length h , mass M , and cross-sectional area A can be computed as the limiting case of the moment of inertia of a cylinder as the radius , so the tensor becomes. Here are some of the most common moments of inertia: Solid cylinder or disk of radius r rotating about its axis of symmetry: Hollow cylinder of radius r rotating about its axis of symmetry: Solid sphere of radius r rotating about its center: Hollow sphere of radius r | {
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"lm_label": "1. YES\n2. YES",
"lm_name": "Qwen/Qwen-72B",
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"url": "http://bfqw.shakemymag.it/moment-of-inertia-cylinder.html"
} |
performance, sql, mysql, unit-testing
Title: Creating many random test database entries I'm working on a simple time sheet webapp. I have created the following query (simplified - I actually have several mapped columns of a similar type to project_id) to generate test data:
INSERT INTO `entries` (`entry_id`, `user_id`, `project_id`, `date`, `comment`, `hours`)
VALUES
( null,
0,
(SELECT `project_id` FROM projects ORDER BY RAND() LIMIT 1),
CURRENT_DATE(),
'# TEST DATA #',
(SELECT ROUND((0.25 + RAND() * (24 - 0.24)), 2))
); | {
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"url": null
} |
java, api, rest, spring
public int updateName(Long id, String name) throws SQLException, ConnectionFailedException {
try (Connection conn = MySqlConn.getConn()) {
String sql = "UPDATE customers " +
"SET name=? " +
"WHERE id=?";
PreparedStatement stmt = conn.prepareStatement(sql);
stmt.setString(1, name);
stmt.setLong(2, id);
int result = this.crud.updateRow(stmt);
conn.commit();
return result;
}
} | {
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"tags": "java, api, rest, spring",
"url": null
} |
quantum-mechanics, operators, commutator, linear-algebra
$$[[\hat{A},\hat{B}], \hat{A}] = 0 \quad \quad \stackrel{\color{red}{?}}{\implies} \quad \quad [\hat{A}, \hat{B}] = 0.$$
But what you have "shown" instead is that:
$$[\hat{A},\hat{B}] = 0 \quad \quad \implies \quad \quad [[\hat{A},\hat{B}], \hat{A}] = 0.$$
But this is pretty trivial, since the commutator of anything with zero is zero!
If you continue your calculation a little further, you should be able to show that:
$$[[\hat{A},\hat{B}], \hat{A}] = 0 \quad \quad \implies \quad \quad [\hat{A}^2, \hat{B}] = 2 \hat{A} \,[\hat{A}, \hat{B}].$$
So yes, $[\hat{A},\hat{B}] = 0$ satisfies this condition, but it isn't the only condition that does. A nice example from introductory Quantum Mechanics is given by @Cream in the same comment: $$[[\hat{x},\hat{p}],\hat{x}] = 0, \quad \quad \text{but} \quad \quad [\hat{x},\hat{p}]\neq 0!$$
However, the above condition is satisfied, since $$[\hat{x}^2, \hat{p}] = 2 \,\hat{x} \,[\hat{x},\hat{p}].$$ | {
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[..]but it seems a bit odd, that such a fast growing sequence is regarded as smaller than $\omega^2$.
Well, that's the thing when dealing with infinities. Sometimes our intuition fails us. While $(\underbrace{2^{2^{2^\ldots}}}_{n\text{-times}})_{n < \omega}$ could be regarded as "a fast growing sequence", each of its elements is finite and therefore $\omega$ is an upper bound. As $\omega$ certainly is the least upper bound, we get $^\omega2 = \omega$.
By an analogous argument we get that $$2^\omega := \sup \{2^n \mid n < \omega \} = \omega$$
So we are left with ordering $\omega, \omega^2, \omega^\omega$ and $^\omega \omega$.
We have \begin{align}\omega^2 &:= \omega \cdot \omega \\ &= \sup \{ w \cdot n \mid n < \omega\} \\ &\ge \omega \cdot 2 \\ &> \omega \end{align}
and
\begin{align}\omega^\omega &= \sup \{ \omega ^n \mid n < \omega \} \\ &\ge \omega^3 \\ &= \sup \{(\omega^2) \cdot n \mid n < \omega \} \\ &\ge \omega^2 \cdot 2 \\ &> \omega^2. \end{align} | {
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"id": null,
"lm_label": "1. YES\n2. YES",
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"openwebmath_score": 1.0000098943710327,
"tags": null,
"url": "https://math.stackexchange.com/questions/1359801/order-of-infinite-countable-ordinal-numbers"
} |
java, beginner, calculator
Class state vs static fields
The one thing that strikes out as odd to me in your code is the heavy reliance on static fields and methods with void return types. This indicates that while you seem to think you need inheritance here (when you don't, see above section), you have forgotten about how to make effective use of class methods to pass information around explicitly, instead choosing to rely on a global state.
From a beginner's point-of-view, I think the biggest obstacle to using static fields (not methods) throughout is that it makes your own code harder to understand in the long run. The reader has to memorize where these fields appear, and how they are modified throughout the codebase. If I may draw from my earlier example again, compare your Multiplications method:
public void basicAdd(){
Result = Result + secondInput;
}
Where are Result and secondInput from, and their type?
How can the method caller retrieve the result of incrementing Result? | {
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"tags": "java, beginner, calculator",
"url": null
} |
java, beginner, algorithm, tree
package binaryTree;
class Node {
Integer data;
Node left;
Node right;
public Node(Integer data, Node left, Node right) {
this.data = data;
this.left = left;
this.right = right;
}
public Node(Integer data) {
this(data, null, null);
}
}
public class BinaryTree {
/**
* Finds the heaviest path in the tree from the given @root Node to a leaf Node.
* @param root
* @return integer representing the sum weight of the heaviest path.
*/
public static int getHeaviestPathWeight(Node root) {
if (root == null)
return 0;
else
return root.data + Math.max(getHeaviestPathWeight(root.left), getHeaviestPathWeight(root.right));
} | {
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"tags": "java, beginner, algorithm, tree",
"url": null
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of phase) Damped Free Vibrations 19 - * With viscous damping due to fluid friction, Substituting x = elt and dividing through by elt yields the characteristic equation, Define the critical damping coefficient such that All vibrations are damped to some. ˆı a) If the block is displaced 3cm to the right and released, for what values of µ will the block remain in that position? g x z A. Simple illustrative example: Spring-mass system 2. In particular we will model an object connected to a spring and moving up and down. This lecture covers: * Viscously Damped Free Vibrations. * Critical Damping. This mechanism, referred to as vortex-induced vibration (VIV), occurs when the vortices, developed in the wake, can couple with the dynamics of the cylinder. All end-of-chapter problems are fully solved in the Solution Manual available only to Instructors. Lecture 6: Damped SHM. Once again, we follow the standard approach to solving problems like this (i) Get a differential equation for s using | {
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"openwebmath_score": 0.46781429648399353,
"tags": null,
"url": "http://harh.bonref.fr/damped-free-vibration-solved-problems.html"
} |
java, performance, array
@Test
public void testGet() {
IntArray ia = new IntArray(100);
assertEquals(0, ia.get(0));
assertEquals(0, ia.getHighWaterMark());
assertEquals(0, ia.get(10000));
assertEquals(10000, ia.getHighWaterMark());
assertEquals(0, ia.set(10000, -1));
assertEquals(-1, ia.get(10000));
}
@Test
public void testPostApply() {
IntArray ia = new IntArray(100);
assertEquals(0, ia.postApply(0, i -> i + 10));
assertEquals(10, ia.get(0));
assertEquals(10, ia.postApply(0, i -> i + 10));
assertEquals(20, ia.get(0));
}
@Test
public void testPreApply() {
IntArray ia = new IntArray(100);
assertEquals(10, ia.preApply(0, i -> i + 10));
assertEquals(10, ia.get(0));
assertEquals(20, ia.preApply(0, i -> i + 10));
assertEquals(20, ia.get(0));
} | {
"domain": "codereview.stackexchange",
"id": 12403,
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"tags": "java, performance, array",
"url": null
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neuroscience, vision, behaviour, neurophysiology, neuroplasticity
Roe AW, Pallas SL, Kwon YH, Sur M. 1992. Visual projections routed to the auditory pathway in ferrets: receptive fields of visual neurons in primary auditory cortex. Journal of Neuroscience, 12(9): 3651-64. | {
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"tags": "neuroscience, vision, behaviour, neurophysiology, neuroplasticity",
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} |
reference-request, machine-learning, artificial-intelligence
"Financial time series forecasting with machine learning techniques: A survey" by Krollner, Vanstone, and Finnie finds:
"...that artificial neural networks (ANNs) are the dominant machine
learning technique in this area."
"Machine Learning Strategies for Time Series Forecasting" by Bontempi, Ben Taieb, and Le Borgne focuses on three aspects:
"...the formalization of one-step forecasting problems as supervised
learning tasks, the discussion of local learning techniques as an
effective tool for dealing with temporal data, and the role of the
forecasting strategy when we move from one-step to multiple-step
forecasting." | {
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"id": 1702,
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"openwebmath_score": null,
"tags": "reference-request, machine-learning, artificial-intelligence",
"url": null
} |
python, beginner, python-2.x, rock-paper-scissors
if user_choice == computer_choice:
print computer_choosed
print "So it's a tie"
play_again()
elif user_choice == 'stone':
if computer_choice == 'paper':
print computer_choosed
print "So, You loose"
play_again()
elif computer_choice == 'scissor':
print computer_choosed
print "So, Cheers! You won!"
play_again()
elif user_choice == 'paper':
if computer_choice == 'scissor':
print computer_choosed
print "So, you loose."
play_again()
elif computer_choice == 'stone':
print computer_choosed
print "So, Cheers! You won!"
play_again() | {
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"tags": "python, beginner, python-2.x, rock-paper-scissors",
"url": null
} |
cell-biology, dna, epigenetics
Is my understanding of epigenetics anywhere close to the truth? Short answer: Yes, epigenetics play a role in determining gene expression, therefore protein expression and function.
Lifestyle factors like diet, smoking, alcohol consumption, and stress can change one's epigenome. A historical example of this might be the Dutch Hunger Winter of 1944-45; there is evidence that after the parents' generation suffered during World War II, the children who were conceived during this time and exposed in utero to famine had different epigenetic marks than their siblings who were conceived not during the famine. | {
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"openwebmath_score": null,
"tags": "cell-biology, dna, epigenetics",
"url": null
} |
ros, calibration, pose, camera
Title: Camera vs world calibration
Hi all!
I'm successfully using a "home made" stereo head to obtain a disparity image with the package stereo_image_proc.
Now I'm trying to calculate the position of the camera in the world frame, possibly using a checkerboard where the first cross represents the world origin.
I've tried to use the camera_pose_calibration package without success.
Do you know others methods that you can suggest me?
I'm particulary interested in online methods where the camera automatically calibrates itself by looking at the checkerboard.
Many thanks!
Originally posted by oleo80 on ROS Answers with karma: 61 on 2012-07-25
Post score: 0
If you have the intrinsics of just one camera, you should be able to use FindExtrinsicCameraParams, which will give the rotation and translation between the checkerboard frame and the camera frame
Check out opencv docs for more info | {
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"tags": "ros, calibration, pose, camera",
"url": null
} |
mars, water
Title: What are the most recent minerals modified by water found to date on Mars? There likely was quite a bit of liquid water on the surface of Mars less than 4 billion years ago. We know this because we found rocks that old that have been modified by the presence of water. For example :
If the martian blueberries, or hematite spherules found by Opportunity formed by slow evaporation in mineral-rich liquid water, they likely formed 3 billion years ago.
Serpentines have been detected by CRISM. | {
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pathology, death
The sum of the groups explains 96.7% of deaths. I think the remaining 3.3% would be other or undetermined causes, and rounding errors in the data. The natural causes accounted for 87.9%, and non-natural causes were 9.1%. The most common causes were cardiovascular diseases, infectious/parasitic diseases, and cancers.
It is difficult to assess how natural the cause of deaths are. For example, many cancers, cardiovascular, and respiratory diseases are more common in obese people and smokers (often self-inflicted damage), nutritional deficiencies are often caused by failing welfare and social systems.
Additionally, among the recorded causes of death in England and Wales in 2011, of the total 484,367 deaths recorded, 17,590* deaths were from extrinsic sources (accidents, homicides etc.). This is around 3.6% of deaths. In this data, the most common causes were cancers (29.6%), circulatory diseases 28.8%, and respiratory diseases (14.0%). | {
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"tags": "pathology, death",
"url": null
} |
nec. I also have to take data still. Optimization is the process of finding the greatest or least value of a function for some constraint, which must be true regardless of the solution. , Samad, T. High School: Functions » Introduction Print this page. • Those in the smoking group smoke a pack a day. 68 Mathematics HL guide Internal assessment Internal assessment criteria The exploration is internally assessed by the teacher and externally moderated by the IB using assessment criteria that relate to the objectives for mathematics HL. To prepare yourself for the Fall. Snowflakes exhibit six-fold radial symmetry, with elaborate, identical patterns on each arm. Note in Figure 9. Example sheets (and other info) for courses offered by DAMTP appear on the DAMTP example sheet page. The first talk typically starts at 11:00 am and the last talk finishes about 5:00 pm. The only real thing that I came up with is something to do with statistics and Pokemon, but those don't seem to work well | {
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"lm_q2_score": 0.8558511543206819,
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"openwebmath_score": 0.3140256106853485,
"tags": null,
"url": "http://hfnl.el-trencito.de/optimization-math-ia-example.html"
} |
r
return(dta_res)
}
Tests
x <- 1:6505
res <- assign_interval(x = x, brackets = list(c(1, 325),
c(1, 651),
c(1, 976),
c(1, 1301),
c(1, 1626),
c(1, 1952))) Maybe it is overkill to use findInterval when your brackets only have two values (a min and a max). I would suggest this much shorter function based on two outer calls with >= and <=. As you probably know, outer is efficient in that it can take advantage of vectorized functions, so here only a single call to <= and >= will be made:
assign_interval2 <- function(x, brackets) {
stopifnot(all(lengths(brackets) == 2L))
lower_bounds <- sapply(brackets, head, 1)
upper_bounds <- sapply(brackets, tail, 1)
outer(x, lower_bounds, ">=") & outer(x, upper_bounds, "<=")
} | {
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"tags": "r",
"url": null
} |
machine-learning, unsupervised-learning, models
Title: How does an unsupervised learning model learn? How does an unsupervised learning model learn, if it does not involve any target values? Supervised learning is typically an attempt to learn a mathematical function, $f(\bf X)=\bf y$. For this, you need both the input vector $\bf X$ and the output vector $\bf y$. The model outputs have whatever dimensionality that the target values have.
Unsupervised learning models instead learn a structure from the data. A clustering model, for example, is learning both how many clusters exist in the data (a number that's not the same type as the inputs) and where those clusters are located (which is also a different type from the inputs). The output of running this model on a new datapoint $x$ is not the same type as $x$, but instead a classification label.
Similarly, time series models learn parameters that symbolize how vectors in the input relate to each other, rather than raw inputs themselves. | {
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"tags": "machine-learning, unsupervised-learning, models",
"url": null
} |
python
Title: Nagios status.dat to dict() - Could it be better? This is something myself and a former colleague were working on and I've finally finished it but wanting to see if we've done as well as we can or if it can be further optimised.
Also looking at doing a new feature for getting a list of all services rather than hosts and find the status of the service on each host.
Here's what I've got to so far:
import sys
import re
import os
def get_nagios_status(path):
"""
Parse the Nagios status.dat file into a dict to give the ability to report on host/service information
`path` is the absolute path to the Nagios status.dat
Return dict() if OK, -1 if not
"""
result = {}
record = {}
mode = ''
parse_enabled = False
try:
f = open(path, 'r')
except:
return -1
try:
for line in f.readlines():
line = line.rstrip() | {
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} |
c++, beginner, console, file
void command::executeCommand(string com)
{
if (com == "getTime")
{
cout << string( 100, '\n' ); //clear screen
SYSTEMTIME t;
GetLocalTime(&t);
cout<< "H:"<<t.wHour<<" M:"<<t.wMinute<<" S:"<<t.wSecond<<endl;
}
if (com == "getCommands")
{
cout << string( 100, '\n' );
printCommands();
}
}
While it is okay to put using namespace std in a local scope (such as a function), it's especially problematic to put it into a header file. By doing this, anyone including it will be forced to have that namespace code exposed globally, and you shouldn't force that on anyone. Although the std namespace is most commonly used, this applies to any of them.
You should be opening the file and doing user input in main(), not within the class. You should be receiving data from a client (such as main()) and constructing an object with this data. | {
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Correction: I accidentally inverted one negation mentally when I thought about this the first time. You’re right about $X$, but not about $\varnothing$. Let $S=\{x\in X:\forall A\in\varnothing(x\in A)\}$; then $S$ is actually $X$, not $\varnothing$. To see this informally, ask yourself how there could be an $x\in X\setminus S$: there would have to be an $x\in X$ such that $\exists A\in\varnothing(x\notin A)$. But there isn’t any $A\in\varnothing$, so there is no such $x$, and $S=X$. (And I see now that Asaf has already pointed this out in his answer.) | {
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"url": "http://math.stackexchange.com/questions/151924/unnecessary-property-in-definition-of-topological-space?answertab=votes"
} |
java
Edit:
I'm sorry... is there anything that u suggest I could do to fix the problem? if there's any.. could you please be specific with the steps? I cannot understand what u r saying.
This is all rather unrelated to ROS, but: for java.lang.ProcessBuilder the following can be found in the documentation:
This class is used to create operating system processes.
[..]
Each process builder manages these process attributes:
[..]
an environment, which is a system-dependent mapping from variables to values. The initial value is a copy of the environment of the current process (see System.getenv()). | {
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"url": null
} |
php, mysql, mysqli
/**
* Creates parameter array to store parameters and a set of references that refers to it.
*
* We create parameter array to store parameters set by the user,
* and we create an array that references those parameters to be
* used as arguments when we use call_user_func() to call
* MySQLi_STMT::bind_param().
*
* @see $params
* @see $references_params
* @see __construct()
*
*/
protected function createParameterVariablesAndReferences()
{
$placeholder_count = count($this->placeholders);
if ($this->statement_object->param_count != $placeholder_count)
{
throw new \RuntimeException("StatementWrapper error, fails to prepare the statement. Parameter count ({$this->statement_object->param_count}) and placeholder count ({$placeholder_count}) does not match.");
}
$this->references_params['types'] = &$this->param_types; | {
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"url": null
} |
javascript, jquery, ajax
But, I find it best practice to keep animations related to a certain set of functionality within their own queues so as to minimize potential conflicts with effects you might add in the future. Like say you added some functionality in the future to change some of other property/class on <body>, if the effects were in their own queue, they could be applied to the element simultaneously with the icon loading effect without causing undesirable interactions (obviously other than if they impact the same CSS properties in the loading class). | {
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} |
c, linked-list, library
if(node->size == SIZE_ZERO) {
void *tmp = node->data;
list->remove(list, 0);
return tmp;
}
void *tmp = cd9list_copyNodeData(node);
list->remove(list, 0);
return tmp;
}
CD9List *cd9list_filter(void *self,
const void *data,
CD9FindCallback cmp)
{
CD9List *list = (CD9List *)self;
CD9List *filteredList = cd9list_createList();
CD9FOREACH_(list, node) {
if(!cmp(node->data, data, node->size)) {
filteredList->appendCopy(filteredList, node->data, node->size);
}
}
return filteredList;
}
CD9List *cd9list_filterByValue(void *self, const void *data)
{
CD9List *list = (CD9List *)self;
CD9List *filtered = cd9list_createList(); | {
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"url": null
} |
electromagnetism, maxwell-equations, electromagnetic-induction
What is happening when delta x of this loop increases? Give me a theoretical idea and how is emf increasing? I know that flux is changing but I think that the rails on which conductor rod is moving is not contributing that much to induced emf
What is induced emf actually in this case is it the energy with which charges are moving or the increasing electric field in conductor because of the charge accumulation at the corners of conductor creating a region acting as source for energy The induced emf blv is called motional emf. thus we are able to produce induced emf by moving a conductor instead of varying magnetic field that is, by changing the magnetic flux enclosed by the circuit. | {
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"tags": "electromagnetism, maxwell-equations, electromagnetic-induction",
"url": null
} |
inorganic-chemistry, analytical-chemistry, crystallography, minerals
Chrysotile: $\ce{(Mg^2+)3[Si2O5]^2−([OH]^−)4}$
Talc A: $\ce{(H+)2(Mg^2+)3([SiO3]^2+)4}$
Talc B: $\ce{(Mg^2+)3[Si4O10]^4−([OH]^−)2}$
So we cannot test for $\ce{Mg^2+}$ or $\ce{[OH]^−}$. But is there a chemical test for $\ce{[Si2O5]^2−}$ that can be done at home? And is it safe to rule out chrysotile if no $\ce{[Si2O5]^2−}$ can be detected, or can the amount be too low for chemical detection but still dangerous?
Is there a chemical test for $\ce{[Si2O5]^2−}$ that can be done at home? | {
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"tags": "inorganic-chemistry, analytical-chemistry, crystallography, minerals",
"url": null
} |
javascript, jquery
ticket.push($("input[name='ticket_eind_tijd\\[\\]']").map(function(){return $(this).val();}).get());
ticket.push($("input[name='ticket_aanal_max\\[\\]']").map(function(){return $(this).val();}).get());
ticket.push($("input[name='ticket_aanal_min\\[\\]']").map(function(){return $(this).val();}).get());
tickets.push(ticket);
});
historyVar['tickets'] = tickets;
}); | {
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"lm_q2_score": null,
"openwebmath_perplexity": null,
"openwebmath_score": null,
"tags": "javascript, jquery",
"url": null
} |
ros2
uri: https://github.com/ros2-gbp/ament_cmake-release.git
version: release/bouncy/ament_cmake_export_include_directories/0.5.1-0
- git:
local-name: ament_cmake/ament_cmake_export_interfaces
uri: https://github.com/ros2-gbp/ament_cmake-release.git
version: release/bouncy/ament_cmake_export_interfaces/0.5.1-0
- git:
local-name: ament_cmake/ament_cmake_export_libraries
uri: https://github.com/ros2-gbp/ament_cmake-release.git
version: release/bouncy/ament_cmake_export_libraries/0.5.1-0
- git:
local-name: ament_cmake/ament_cmake_export_link_flags
uri: https://github.com/ros2-gbp/ament_cmake-release.git
version: release/bouncy/ament_cmake_export_link_flags/0.5.1-0
- git:
local-name: ament_cmake/ament_cmake_gmock
uri: https://github.com/ros2-gbp/ament_cmake-release.git
version: release/bouncy/ament_cmake_gmock/0.5.1-0
- git:
local-name: ament_cmake/ament_cmake_gtest
uri: https://github.com/ros2-gbp/ament_cmake-release.git | {
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} |
c#, beginner, object-oriented, entity-framework-core
public void LoadContract(int id)
{
Stopwatch stopwatch = new Stopwatch();
stopwatch.Start();
using (ModelContext model = new ModelContext())
{
Contract = model.Contracts
.Where(c => c.Id == id)
.Include(w => w.WorkerNavigation)
.ThenInclude(w => w.IssuedNavigation)
.Include(w => w.WorkerNavigation)
.ThenInclude(w => w.BankNavigation)
.Include(lkw => lkw.ListKindWorks)
.ThenInclude(lkw => ((ListKindWorks)lkw).IdKindWorkNavigation)
.Include(ls => ls.ListSubjects)
.ThenInclude(ls => ((ListSubjects)ls).IdSubjectNavigation)
.Single();
}
stopwatch.Stop();
logger.Debug("Загрузка договора для экспорта: {0}", stopwatch.Elapsed);
} | {
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So the question we should ask is why are the precision and recall always the same. If the precision and recall are always the same, then their definition should be identical. Let's see if we can simplify their identity. $$P = R \\ \frac{\sum_{l\in L}{{TP}_l}}{\sum_{l\in L}{({TP}_l + {FP}_l)}} = \frac{\sum_{l\in L}{{TP}_l}}{\sum_{l\in L}{({TP}_l + {FN}_l)}} \\ \sum_{l\in L}{({TP}_l + {FP}_l)} = \sum_{l\in L}{({TP}_l + {FN}_l)} \\ \sum_{l\in L}{{TP}_l} + \sum_{l\in L}{{FP}_l} = \sum_{l\in L}{{TP}_l} + \sum_{l\in L}{{FN}_l} \\ \sum_{l\in L}{{FP}_l} = \sum_{l\in L}{{FN}_l}$$
So it all boils down to whether or not the sum of each label's false positives is always equal to the sum of each label's false negatives. Let's say that you have the following row in the first table:
predtrue
AB | {
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"lm_q1_score": 0.9546474155747541,
"lm_q1q2_score": 0.8114227879685589,
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"openwebmath_score": 0.8286980986595154,
"tags": null,
"url": "https://geekyisawesome.blogspot.com/"
} |
quantum-mechanics, photoelectric-effect
Title: How are photons arranged in a light ray? Title, or more specifically, if a constant light source is directed onto a flat surface, would the photons spread equally on said surface? In addition, say, at the beginning, 10 photons reached the surface, would it still be 10 photons reaching the surface after a split second?
I just came this up when after watching a photoelectric effect experiment presented by Khan Academy. Any help is very appreciated. Well, I think your question is in fact about flux of photons, namely, a number of photons reaching a certain cross section during a certain time interval. Say, million of photons reaching one square meter surface in one second. | {
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"tags": "quantum-mechanics, photoelectric-effect",
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} |
solar-system, comets, kuiper-belt, 9th-planet
The properties you can obtain about the ninth planet, if it exists, from large amount of data on non-periodic comets are: | {
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} |
classical-mechanics, lagrangian-formalism, hamiltonian-formalism, action, constrained-dynamics
\begin{align*}
-d\mathcal{A} &= -d\lambda\ (H - E) - d\theta \cdot P - d\omega \cdot L.
\end{align*}
This, it seems to me, is (apart from a sign) the differential almost hamiltonian (as cited on page 32). Also I have changed notation: I write $d\lambda$ instead of $d\chi$. That is because I think at this stage of the dirac-analysis, $d\lambda$ is either arbitrary (gauge parameter) or will be constrained as a result of the diract consisteny algorithm. I has not yet the meaning of the "differential of the instant" (page 27)
\begin{align}
d\chi := \frac{\sqrt{\frac{1}{2}\sum_i m_i \| \mathfrak{D}q^i \|^2 }}{\sqrt{E - V}}. \tag{58}
\end{align}
As defined above, $d\chi$ depends upon the "velocities" $dq^i$, and those shall not appear explicitly in the hamiltonian. But somehow, the above expression for $d\chi$ should reappear in the hamiltonian anaylsis ?!
I hoped that it will appear through the dirac constraint analysis (constraints shall propagate), but sofar I only got | {
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"tags": "classical-mechanics, lagrangian-formalism, hamiltonian-formalism, action, constrained-dynamics",
"url": null
} |
ros2
Title: ros2 launch using ignition while run command line in ros2
How do you load some command line such as "ros2 topic pub --once /S0 std_msgs/msg/Float64 '{data: 1.5}' && ros2 topic pub --once /S1 std_msgs/msg/Float64 '{data: 1.5}'" while leave ignition bridge in the launch file?
Even better, how do you create a node where you can load ros2 command line?
Originally posted by kak13 on ROS Answers with karma: 113 on 2022-02-07
Post score: 0
Original comments
Comment by ChuiV on 2022-02-09:
I'm not sure I follow your question. Are you asking how to run ros2 topic pub ... from a launch file? If so, use the launch.actions.ExecuteProcess action.
Comment by kak13 on 2022-02-14:
Yes!! I think that's the one.
How do you use it exactly? I don't think I've ever seen it before
Sounds like you're looking for the ExecuteProcess Launch action:
from launch import LaunchDescription
from launch.action import ExecuteProcess | {
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waves, frequency, coherence
$I=I_1 + I_2$
This is the fundamental difference between incoherent and coherent radiation. The same phenomenon actually governs the transition between quantum and classical world. Classical world emerges from quantum world when you discard the phases, which are rapidly varying and can't be observed in macroscopic situations. | {
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} |
classical-mechanics, angular-momentum
If the net external torque on an N particle system is 0, the system's total angular momentum $\vec{L} = \sum \vec{r}_\alpha \times \vec{p}_\alpha$
My problem is that when he discusses Kepler's Second Law (pg. 93), he shows that the area sweeped by a line connecting a planet to the sun is the same in any time interval $dt$:
$$ \frac{dA}{dt} = \frac{1}{2m} | \vec{r} \times \vec{p}| = \frac{1}{2m} |\vec{l}|$$
he states that because the angular momentum is conserved, $\frac{dA}{dt}$ is constant. This seems like it doesn't match with his principle as it is only the magnitude conserved and not the vector itself. So I'm confused as to which it is. Any clarification is appreciated. The angular momentum vector, which is perpendicular to the plane of motion, is conserved. So its magnitude is conserved, and hence the rate of sweeping out area. | {
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between two consecutive values of the sequence ( d ), and the number of steps ( n ). The values $${a_n} = f\left( n \right)$$ taken by the function are called the terms of the sequence. Conic Sections Trigonometry. A geometric sequence has the form: a 1, a 1 r, a 1 r 2, a_1, a_1 r, a_1 r^2, You need to provide the first term of the sequence ( ), the constant ratio between two consecutive values of the sequence (. Fibonacci sequence table. 免费的级数收敛计算器 - 一步步检验无穷级数的收敛性. Learn about the Golden Ratio, how the Golden Ratio and the Golden Rectangle were used in classical architecture, and how they are surprisingly related to the famed Fibonacci Sequence. Determines convergence or divergence of an infinite series. Determine whether or not the series converge using the appropriate convergence test (there may be more than one applicable test. The partial sums of a series form a new sequence, which is denoted as {s 1, s 2, s 3, s 4,}. We have seen that, in general, for a given series , This | {
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"openwebmath_score": 0.89300936460495,
"tags": null,
"url": "http://volv.casandrea.it/sequence-calculator-convergence.html"
} |
mechanical-engineering, vibration, product-testing
Second, what kind of thing are you designing? A mass produced near-commodity product, say something along the lines of a cheap clock radio? Or is it a unique high cost item, like a satellite that can't be damaged in testing? Or something in the middle of that spectrum? How much are you willing to invest in testing? How much are your customers willing to pay for the resulting reliability? At a certain point, it's better to simply replace/repair a product than it is to design the thing that will last forever. | {
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"url": null
} |
general-relativity, spacetime, wormholes
QUESTION.
Can a detour through a wormhole really be shorter in distance or time than the straight line path?
As the spacetime metric is a pseudo-metric (distance can be negative), I realise that triangle inequality will probably no longer apply. Is that the reason why wormholes can allow a faster journey between the two points? There has been research on this lately:
https://arxiv.org/abs/1608.05687
https://arxiv.org/abs/2008.06618
I'm no expert on this, but I think that any time a physically realizeable traversible wormhole is found, it somehow always takes longer than taking the scenic route (in the frame of the outside observer). That's a good thing. We don't want to violate causality. | {
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"lm_q1q2_score": null,
"lm_q2_score": null,
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"openwebmath_score": null,
"tags": "general-relativity, spacetime, wormholes",
"url": null
} |
classical-mechanics, coordinate-systems, hamiltonian-formalism, phase-space, poisson-brackets
But since this is a fundamental poisson bracket, this should give 1. Where have I made a mistake? The total derivative $\frac{dP}{dP} = \frac{\partial P}{\partial p}\frac{\partial p}{\partial P} + \frac{\partial P}{\partial q}\frac{\partial q}{\partial P}$ equals 1, not the partial derivative $\frac{\partial P}{\partial p}\frac{\partial p}{\partial P}$. | {
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inorganic-chemistry, halides, reactivity, electronegativity
Next to fly out is reactivity: what is reactivity? Perhaps the total energy released in spontaneous reaction(s)? Obviously, you want to compare reactivity - but how completely? Would you require data for all possible reactions of each halogen with all other reagents and then average the data? Probably not, just get a "more than" or "less than" comparison for a few reactions of the halogens.
The hydrogen-halogen and carbon-halogen bond energies do drop smoothly down the column, as does the electronegativity (the columns of data are for F, Cl, Br and I from left to right) (Ref 2): And the last line is another set of electronegativity numbers, from a different set of data points. | {
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} |
fluid-dynamics, energy, conservation-laws
\end{eqnarray}
What is the total mechanical energy of the system? I would take energy as solely kinetic energy of the system.
\begin{eqnarray}
E = \sum\frac{1}{2}\rho u^2
\end{eqnarray}
It seems that this definition is incorrect as if we start with a system of initial density variation $\rho(x,0) = \rho(x)$ and zero velocity everywhere $u(x,0)= 0$ then we start with zero kinetic energy and zero total energy. But from the mass and momentum balance equations it is clear that there will motion in fluid due to density variations. So we have higher energy than we started with.
What is wrong with definition of total energy I am assuming? which part of the energy should be taken into account? 1) There is no "total mechanical energy", there is only mechanical energy and total energy. Only total energy
$$
E =\int d^3x\, \left({\cal E}_{int}+\frac{1}{2}\rho v^2\right)
$$ | {
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"tags": "fluid-dynamics, energy, conservation-laws",
"url": null
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tutorial, using the matrix multiplication example from class, follow this link to a FAQ. MPI matrix output by. The resulting matrix agrees with the result of composition of the linear transformations represented by the two original matrices. To scale, I am using a kind of domain decomposition(DD), so that part is on MPI. The experimental results validate the high performance gained with parallel processing OMP as compared to the traditional sequential execution of matrix multiplication. Abstract: We present efficient parallel matrix multiplication algorithms for linear arrays with reconfigurable pipelined bus systems (LARPBS). This is what i have so far #include "mpi. Now, process in the grid is assigned the blocks of each matrix. tributed to meshes of nodes (e. Title: Matrix Vector Multiplication 1 Matrix Vector Multiplication 2 Sequential Algorithm 3 Decomposition of Matrices. rows Let C be a new n n matrix For i=1 to n For j=1 to n Cij=0 For k=1 to n Cij=Cij + aik bkj Fig. An LARPBS | {
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"url": "http://puntoopera.it/ruym/mpi-block-matrix-multiplication.html"
} |
human-anatomy, neuroanatomy, eyes, neurology
The photoreceptor layer is thicker, up to 7 or 8 cell bodies deep. This means higher photoreceptor density.
The outer plexiform layer (photoreceptors to bipolar cell connections) is considerably thicker. A single cone should connect to fewer bipolar cells in the retina, so how does this make sense? We'll find the answer in #3.
The outer nuclear layer is only one cell thick. This is the first layer that is actually thinner in the foveal region. The cell bodies for photoreceptors from tis region have been displaced laterally, and the outer plexiform layer from #2 had to be larger to accommodate this lateral shift
The inner plexiform layer, connections between bipolar cells and ganglion cells, is nonexistent. Also absent is the ganglion cell layer itself. | {
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"tags": "human-anatomy, neuroanatomy, eyes, neurology",
"url": null
} |
c#, singleton
Title: Correct usage for singleton and reusability? I've made the following DataSetReader, DS Attribute, and DataSetManager.
My main concerns are the following:
This is my first time using a Singleton. Should I? And have I done it well?
My aim is to make this class reusable in other projects. Is there anything I should improve to allow for this further? I pulled the logic for handling DBNull value into the Singleton I created. Is there anything else I can or should do?
DataSetReader:
public class DataSetReader<T> where T : new()
{
#region Events
/// <summary>
/// Fires when a column is found in the DataSet but not in Object, T.
/// </summary>
public event InvalidValueHandler ColumnNotFound;
protected virtual void OnColumnNotFound(DataColumn column, ref Object value)
{
if (ColumnNotFound != null)
ColumnNotFound(this, column, ref value);
} | {
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} |
Warm Up 3-3 2. \bigg(\dfrac{\textcolor{red}{a}}{\textcolor{blue}{b}}\bigg)^\textcolor{limegreen}{c}= \dfrac{\textcolor{red}{a}^\textcolor{limegreen}{c}}{\textcolor{blue}{b}^\textcolor{limegreen}{c}}, \bigg(2\dfrac{\textcolor{red}{3}}{\textcolor{blue}{4}}\bigg)^\textcolor{limegreen}{5} = \bigg(\dfrac{\textcolor{red}{11}}{\textcolor{blue}{4}}\bigg)^\textcolor{limegreen}{5} = \bigg(\dfrac{\textcolor{red}{11}^\textcolor{limegreen}{5}}{\textcolor{blue}{4}^\textcolor{limegreen}{5}}\bigg). MATH POWER! Could please explain me ?Thanks. This … If there is any doubt that it could be negative, then we’d refrain from doing it. . Solution: We know, b-n = 1/b n. So, 3-4 = 1/3 4 = 1/81. Download a PDF of free latest Sample questions with solutions for Class 8, Math, CBSE- Exponents and Powers . Simplify [10 [ (216)1/3 + (64)1/3 ]3 ] 3/4, Problem 4. Math can be a difficult subject for many students, but luckily we’re here to help. If so then you must have a knack for tackling some problems believed to | {
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"lm_q1_score": 0.9511422241476943,
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"lm_q2_score": 0.888758793492457,
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"openwebmath_score": 0.6109035611152649,
"tags": null,
"url": "https://mindwink.com/morris-college-zxzz/power-questions-maths-0f51b3"
} |
imu, ubuntu, xsens, ros-fuerte, ubuntu-precise
ROS Master does not appear to be running.
Online graph checks will not be run.
ROS_MASTER_URI is [http://localhost:11311]
lsi-ros@lsi-ros:~$
Is it possible the problem is the PYTHONPATH /opt/ros/fuerte/share/ros/core/roslib/src ??
How can I fix it?
Edit2:
The line error 63 is:
self.device.write(msg)
if verbose:
print "MT: Write message id 0x%02X (%s) with %d data bytes: [%s]"%
(mid, getMIDName(mid), length,
' '.join("%02X"% v for v in data)) | {
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"tags": "imu, ubuntu, xsens, ros-fuerte, ubuntu-precise",
"url": null
} |
# how to prove the relation between the floor function and the number of divisors
I am trying to get an intuitive meaning (a proof) or why the following is true. $$\sum_{k = 1}^n \sum_{d|k} 1 = \sum_{d = 1}^n \left[\frac{n}{d} \right]$$
I know that $f(x) = [x] = \sum_{n \leq x} 1$ but I can't see it in the case of a fraction.
Edit: can someone please tell me what I am doing wrong. I believe its something to do with summations. I know the divisor function $\tau(k) = \sum_{d|k} 1$ so consider $$\sum_{n \leq x} \tau(n) = \sum_{n \leq x}\sum_{d|n} 1 = \sum_{n \leq x} \left[ \frac{x}{n} \right]$$ so this must mean $$\sum_{d|n} 1 = \left[ \frac{x}{n} \right]$$ which is clearly false. So what am I missing?
-
Regarding your "Edit". It's not true that if the sum of F is equal to the sum of G, then F = G. – user58512 Mar 23 '13 at 1:51
I see. Thank you. – Tyler Hilton Mar 23 '13 at 1:53
Consider first $$\sum_{k=1}^n \sum_{d|k} 1$$
Here is a table | {
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"url": "http://math.stackexchange.com/questions/338432/how-to-prove-the-relation-between-the-floor-function-and-the-number-of-divisors"
} |
python, python-3.x, excel, web-scraping
Title: Writing and saving scraped documents in several sheets in an Excel file I've written some code in Python for the purpose of scraping names and URLs from several links found in the left sided bar in a webpage and populate the data in several sheets (also giving each sheet a new name taking a customized portion from URL) in an Excel workbook so that things do not get messy and the data can be located separately. I tried to do the whole thing accurately and found it working great. It would be very nice if I get any better idea other than what I did here.
Here is what I tried with:
import requests
from lxml import html
from pyexcel_ods3 import save_data
web_link = "http://www.wiseowl.co.uk/videos/"
main_url = "http://www.wiseowl.co.uk"
def get_links(page): | {
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"openwebmath_perplexity": null,
"openwebmath_score": null,
"tags": "python, python-3.x, excel, web-scraping",
"url": null
} |
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