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number which is a categorical variable which you get down so from a simple neuron we will | |
parameters connected to one parameter and it can even go down by a successive stages | |
of parametric connections which goes down and finally is what enters into what we call | |
and what this does is that we define something as a neural network and then say that this | |
neural network is able to classify images and as we go down over there now one important | |
fact which you will have to take care over here is that as we are learning over here | |
then that would mean that somehow with experience going by that definition somehow with experience | |
which we are gaining we will be able to do that task much better | |
so that means necessarily that as we show it more number of samples of features and | |
which are associated number of categorical variables over there then this whole network | |
over here which i call as a neural network would be able to really associate any unknown | |
this learning you will have to go down through the way of gradient checking and optimizations | |
this so we have the mathematical equation but lets lets get down into what it looks | |
like so say i have three different variables x one x two and x three and these can be three | |
the image and say over here is the average entropy of the image ok so we can have three | |
different features over there for one single image given down now once we have these three | |
of the image x three is also scalar and now together what we can do is we can associate | |
with certain vector and then we can sort of sum them up ok so x one will be multiplied | |
by a weight w one x two will be multiplied by a weight w two x three will be multiplied | |
then my output over here so the form of y is something which is written down as w naught | |
will be a n plus one term summation which comes down over here now from there as we | |
sort of a matrix representation is what is given down over here ok so what w is basically | |
and that is equal to w naught itself and x is another vector of all the ah scalars which | |
are arranged in terms of a matrix over there so this is a matrix form of representation | |
now once i have that one what i can do is i can relate this y to my predicted class | |
this f n l can have two different forms some common forms are something like this the first | |
my x s over here i dont have any sort of a control over my x so these can be anything | |
from minus infinity to plus infinity for the purpose of simplicity we keep down the fact | |
that let these be real valued numbers and not complex valued numbers that that does | |
to plus infinity now that i have these also open ranged then what i get down from this | |
to me that can be anything from minus infinity to plus infinity which would typically make | |
just put a threshold over there say that if the value is greater than zero make it one | |
of functions say a sigmoid non linearity so what it would do is that as my y becomes tending | |
now in the same way as i go with my second non linearity which is called as a tan hyperbolic | |
so you can put down your values of y is varying from minus infinity to plus infinity and you | |
can very intuitively see that as the value of y goes down to minus infinity this value | |
tends to minus one as the value goes to plus infinity this value tends to plus one and | |
say just give down the argument that if it is greater than zero make it one less than | |
i have three scalar values over here so what i can do is i can associate it to some different | |
number of patterns which i want to different number of predictors which i want to do so | |
being the contrast and x three being the average entropy on the image i want to classify whether | |
that is a ball in the image yes or no and whether the image is a photograph or image | |
down subscripted dually now with it with this dual weight subscription what happens technically | |
which i want to classify and the first subscript is the one which connects down which feature | |
is being connected to which target neuron over here ok | |
done for y one and p one in terms of an equation now if i get down another parameter p two | |
and thats what i was saying that do you have another different thing to predict and that | |
may be that whether its a natural image or this was a sketched image now for that you | |
will have a similar set of equation which you get down over here now you can clearly | |
outputs can be designed over here | |
now similarly i can extend it to some n number of some some k number of neurons over here | |
now once you stand on all the row vectors you get down a rectangular matrix over there | |
equation and then accordingly your predicted neurons will also be stacked into one single | |
was applied on a scalar and thats why this can be extended on to a matrix valued form | |
function and that will give you the same sort of a vector output which comes down over here | |
now essentially what this helps you is that you can relate down some j number of input | |
neurons to some k number of output neurons in in straight simple terms now from there | |
once you are able to relate it down next what comes down is that i will have certain sort | |
of error when i am able to relate it down it means that so using these three features | |
and some combination of weights which are present over here i will be able to predict | |
and there is a value which is coming down from this neuron itself ok now the difference | |
between the true value say in the first case there was a ball but it predicted there wasnt | |
a ball so there is its an error its a clear case of an error so but here what i would | |
get done is that the error value is one ok in the other way round where say there wasnt | |
the ground truth also says that there isnt a ball it means that it is ah its its a correct | |
case so similarly we will have it for the second predictor as well now if you see all | |
of these predictors are independent of each other so it means that the errors are also | |
distance between the predicted vector over here this p that becomes a matrix | |
now and the actual ground truth which is so between your p hat and your p so this will | |
learning over here is in a sense that i should be somehow able to get down a network such | |
essentially happens in that case is we use a method called as error back propagation | |
so what it would do is say i have a set of observations x one ok so this one over here | |
is no more related to one particular feature but that one which we are putting down over | |
here in this relationship is actually which is related down to | |
truth and i have my predicted value similarly i keep on doing such that i have n number | |
of images in something which is called as a training set so what happens in a training | |
set in this kind of a problem which is a supervised learning problem is that you have a set of | |
images some n number of images and for each image you also know what is the class label | |
given to it so here we were asking down two questions whether this there is a ball in | |
image kind of thing | |
so there are two vectors over here which i there is a two dimensional vector or two parameters | |
which i want to predict down to class levels so that should also be known to me so there | |
training set ok now on the other side i am going to predict out all of this with a certain | |
given form of my weights over there now initially what i would do is i would start with a neural | |
difference is coming down for each so i get the euclidean distance for each sample so | |
for x one x two x three similarly it up to x n i get down this difference coming down | |
you look carefully into this one | |
so my p hats are what are dependent on all my excess over here ok but these x values | |
they dont change in the whole data set right the only thing which changes within the network | |
the whole objective is that i want to get down a particular value of w which is the | |
only thing variable and adjustable within my neural network such that my cost function | |
over here is minimum and this has to be minimum when you need to have done the minimum error | |
over there as you get down your minimum error in this case this has to be zero so your jw | |
start with a random guess of w within a k th iteration so my k at the start of it will | |
be k equal to zero ok so at k equal to zero i start with some w over here now with that | |
w i will be able to get down my these predictions over here p one to p n hat from there i would | |
is a partial derivative of the cost function with respect to my weight at that particular | |
of these predictions from there i would get down get down as the j w for w k plus one | |
and then i would iterate it over such that at some point of time i would reach down this | |
minimum value of w and then just stop over here ok |
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