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3,001 | Radiosity is a method which attempts to simulate the way in which directly illuminated surfaces act as indirect light sources that illuminate other surfaces. This produces more realistic shading and seems to better capture the 'ambience' of an indoor scene. A classic example is a way that shadows 'hug' the corners of ... |
3,002 | The optical basis of the simulation is that some diffused light from a given point on a given surface is reflected in a large spectrum of directions and illuminates the area around it. |
3,003 | The simulation technique may vary in complexity. Many renderings have a very rough estimate of radiosity, simply illuminating an entire scene very slightly with a factor known as ambiance. However, when advanced radiosity estimation is coupled with a high quality ray tracing algorithm, images may exhibit convincing rea... |
3,004 | In advanced radiosity simulation, recursive, finite-element algorithms 'bounce' light back and forth between surfaces in the model, until some recursion limit is reached. The colouring of one surface in this way influences the colouring of a neighbouring surface, and vice versa. The resulting values of illumination thr... |
3,005 | Due to the iterative/recursive nature of the technique, complex objects are particularly slow to emulate. Prior to the standardization of rapid radiosity calculation, some digital artists used a technique referred to loosely as false radiosity by darkening areas of texture maps corresponding to corners, joints and rece... |
3,006 | Radiosity calculations are viewpoint independent which increases the computations involved, but makes them useful for all viewpoints. If there is little rearrangement of radiosity objects in the scene, the same radiosity data may be reused for a number of frames, making radiosity an effective way to improve on the flat... |
3,007 | Because of this, radiosity is a prime component of leading real-time rendering methods, and has been used from beginning-to-end to create a large number of well-known recent feature-length animated 3D-cartoon films. |
3,008 | One problem that any rendering system must deal with, no matter which approach it takes, is the sampling problem. Essentially, the rendering process tries to depict a continuous function from image space to colors by using a finite number of pixels. As a consequence of the Nyquist–Shannon sampling theorem , any spati... |
3,009 | If a naive rendering algorithm is used without any filtering, high frequencies in the image function will cause ugly aliasing to be present in the final image. Aliasing typically manifests itself as jaggies, or jagged edges on objects where the pixel grid is visible. In order to remove aliasing, all rendering algorit... |
3,010 | Due to the large number of calculations, a work in progress is usually only rendered in detail appropriate to the portion of the work being developed at a given time, so in the initial stages of modeling, wireframe and ray casting may be used, even where the target output is ray tracing with radiosity. It is also commo... |
3,011 | For real-time, it is appropriate to simplify one or more common approximations, and tune to the exact parameters of the scenery in question, which is also tuned to the agreed parameters to get the most 'bang for the buck'. |
3,012 | The implementation of a realistic renderer always has some basic element of physical simulation or emulation – some computation which resembles or abstracts a real physical process. |
3,013 | The term "physically based" indicates the use of physical models and approximations that are more general and widely accepted outside rendering. A particular set of related techniques have gradually become established in the rendering community. |
3,014 | The basic concepts are moderately straightforward, but intractable to calculate; and a single elegant algorithm or approach has been elusive for more general purpose renderers. In order to meet demands of robustness, accuracy and practicality, an implementation will be a complex combination of different techniques. |
3,015 | Rendering research is concerned with both the adaptation of scientific models and their efficient application. |
3,016 | This is the key academic/theoretical concept in rendering. It serves as the most abstract formal expression of the non-perceptual aspect of rendering. All more complete algorithms can be seen as solutions to particular formulations of this equation. |
3,017 | Meaning: at a particular position and direction, the outgoing light is the sum of the emitted light and the reflected light. The reflected light being the sum of the incoming light from all directions, multiplied by the surface reflection and incoming angle. By connecting outward light to inward light, via an intera... |
3,018 | The bidirectional reflectance distribution function expresses a simple model of light interaction with a surface as follows: |
3,019 | Light interaction is often approximated by the even simpler models: diffuse reflection and specular reflection, although both can ALSO be BRDFs. |
3,020 | Rendering is practically exclusively concerned with the particle aspect of light physics – known as geometrical optics. Treating light, at its basic level, as particles bouncing around is a simplification, but appropriate: the wave aspects of light are negligible in most scenes, and are significantly more difficult to... |
3,021 | Though it receives less attention, an understanding of human visual perception is valuable to rendering. This is mainly because image displays and human perception have restricted ranges. A renderer can simulate a wide range of light brightness and color, but current displays – movie screen, computer monitor, etc. – ... |
3,022 | Mathematics used in rendering includes: linear algebra, calculus, numerical mathematics, signal processing, and Monte Carlo methods. |
3,023 | Rendering for movies often takes place on a network of tightly connected computers known as a render farm. |
3,024 | The current state of the art in 3-D image description for movie creation is the Mental Ray scene description language designed at Mental Images and RenderMan Shading Language designed at Pixar . |
3,025 | Other renderers can and are sometimes used, but most other renderers tend to miss one or more of the often needed features like good texture filtering, texture caching, programmable shaders, highend geometry types like hair, subdivision or nurbs surfaces with tesselation on demand, geometry caching, raytracing with ge... |
3,026 | Computer simulations are realized by running computer programs that can be either small, running almost instantly on small devices, or large-scale programs that run for hours or days on network-based groups of computers. The scale of events being simulated by computer simulations has far exceeded anything possible usi... |
3,027 | Because of the computational cost of simulation, computer experiments are used to perform inference such as uncertainty quantification. |
3,028 | A model consists of the equations used to capture the behavior of a system. By contrast, computer simulation is the actual running of the program that perform algorithms which solve those equations, often in an approximate manner. Simulation, therefore, is the process of running a model. Thus one would not "build a sim... |
3,029 | Computer simulation developed hand-in-hand with the rapid growth of the computer, following its first large-scale deployment during the Manhattan Project in World War II to model the process of nuclear detonation. It was a simulation of 12 hard spheres using a Monte Carlo algorithm. Computer simulation is often used as... |
3,030 | The external data requirements of simulations and models vary widely. For some, the input might be just a few numbers , while others might require terabytes of information . |
3,031 | Input sources also vary widely: |
3,032 | Lastly, the time at which data is available varies: |
3,033 | Because of this variety, and because diverse simulation systems have many common elements, there are a large number of specialized simulation languages. The best-known may be Simula. There are now many others. |
3,034 | Systems that accept data from external sources must be very careful in knowing what they are receiving. While it is easy for computers to read in values from text or binary files, what is much harder is knowing what the accuracy of the values are. Often they are expressed as "error bars", a minimum and maximum deviati... |
3,035 | Models used for computer simulations can be classified according to several independent pairs of attributes, including: |
3,036 | Another way of categorizing models is to look at the underlying data structures. For time-stepped simulations, there are two main classes: |
3,037 | For steady-state simulations, equations define the relationships between elements of the modeled system and attempt to find a state in which the system is in equilibrium. Such models are often used in simulating physical systems, as a simpler modeling case before dynamic simulation is attempted. |
3,038 | Formerly, the output data from a computer simulation was sometimes presented in a table or a matrix showing how data were affected by numerous changes in the simulation parameters. The use of the matrix format was related to traditional use of the matrix concept in mathematical models. However, psychologists and others... |
3,039 | Similarly, CGI computer simulations of CAT scans can simulate how a tumor might shrink or change during an extended period of medical treatment, presenting the passage of time as a spinning view of the visible human head, as the tumor changes. |
3,040 | Other applications of CGI computer simulations are being developed to graphically display large amounts of data, in motion, as changes occur during a simulation run. |
3,041 | Generic examples of types of computer simulations in science, which are derived from an underlying mathematical description: |
3,042 | Specific examples of computer simulations include: |
3,043 | Notable, and sometimes controversial, computer simulations used in science include: Donella Meadows' World3 used in the Limits to Growth, James Lovelock's Daisyworld and Thomas Ray's Tierra. |
3,044 | In social sciences, computer simulation is an integral component of the five angles of analysis fostered by the data percolation methodology, which also includes qualitative and quantitative methods, reviews of the literature , and interviews with experts, and which forms an extension of data triangulation. Of course, ... |
3,045 | Computer simulations are used in a wide variety of practical contexts, such as: |
3,046 | The reliability and the trust people put in computer simulations depends on the validity of the simulation model, therefore verification and validation are of crucial importance in the development of computer simulations. Another important aspect of computer simulations is that of reproducibility of the results, meanin... |
3,047 | Vehicle manufacturers make use of computer simulation to test safety features in new designs. By building a copy of the car in a physics simulation environment, they can save the hundreds of thousands of dollars that would otherwise be required to build and test a unique prototype. Engineers can step through the simula... |
3,048 | Computer graphics can be used to display the results of a computer simulation. Animations can be used to experience a simulation in real-time, e.g., in training simulations. In some cases animations may also be useful in faster than real-time or even slower than real-time modes. For example, faster than real-time anima... |
3,049 | In debugging, simulating a program execution under test can detect far more errors than the hardware itself can detect and, at the same time, log useful debugging information such as instruction trace, memory alterations and instruction counts. This technique can also detect buffer overflow and similar "hard to detect... |
3,050 | Although sometimes ignored in computer simulations, it is very important to perform a sensitivity analysis to ensure that the accuracy of the results is properly understood. For example, the probabilistic risk analysis of factors determining the success of an oilfield exploration program involves combining samples from... |
3,051 | A multi-core processor implements multiprocessing in a single physical package. Designers may couple cores in a multi-core device tightly or loosely. For example, cores may or may not share caches, and they may implement message passing or shared-memory inter-core communication methods. Common network topologies used t... |
3,052 | Multi-core processors are widely used across many application domains, including general-purpose, embedded, network, digital signal processing , and graphics . Core count goes up to even dozens, and for specialized chips over 10,000, and in supercomputers the count can go over 10 million . |
3,053 | The improvement in performance gained by the use of a multi-core processor depends very much on the software algorithms used and their implementation. In particular, possible gains are limited by the fraction of the software that can run in parallel simultaneously on multiple cores; this effect is described by Amdahl's... |
3,054 | The parallelization of software is a significant ongoing topic of research. Cointegration of multiprocessor applications provides flexibility in network architecture design. Adaptability within parallel models is an additional feature of systems utilizing these protocols. |
3,055 | In the consumer market, dual-core processors started becoming commonplace in the late 2000s. Quad-core processors were also being adopted for higher-end systems. In the late 2010s, hexa-core started entering the mainstream. |
3,056 | The terms multi-core and dual-core most commonly refer to some sort of central processing unit , but are sometimes also applied to digital signal processors and system on a chip . The terms are generally used only to refer to multi-core microprocessors that are manufactured on the same integrated circuit die; separate... |
3,057 | In contrast to multi-core systems, the term multi-CPU refers to multiple physically separate processing-units . |
3,058 | The terms many-core and massively multi-core are sometimes used to describe multi-core architectures with an especially high number of cores . |
3,059 | Some systems use many soft microprocessor cores placed on a single FPGA. Each "core" can be considered a "semiconductor intellectual property core" as well as a CPU core. |
3,060 | While manufacturing technology improves, reducing the size of individual gates, physical limits of semiconductor-based microelectronics have become a major design concern. These physical limitations can cause significant heat dissipation and data synchronization problems. Various other methods are used to improve CPU p... |
3,061 | Several business motives drive the development of multi-core architectures. For decades, it was possible to improve performance of a CPU by shrinking the area of the integrated circuit , which reduced the cost per device on the IC. Alternatively, for the same circuit area, more transistors could be used in the design, ... |
3,062 | As the rate of clock speed improvements slowed, increased use of parallel computing in the form of multi-core processors has been pursued to improve overall processing performance. Multiple cores were used on the same CPU chip, which could then lead to better sales of CPU chips with two or more cores. For example, Inte... |
3,063 | Since computer manufacturers have long implemented symmetric multiprocessing designs using discrete CPUs, the issues regarding implementing multi-core processor architecture and supporting it with software are well known. |
3,064 | Additionally: |
3,065 | In order to continue delivering regular performance improvements for general-purpose processors, manufacturers such as Intel and AMD have turned to multi-core designs, sacrificing lower manufacturing-costs for higher performance in some applications and systems. Multi-core architectures are being developed, but so are ... |
3,066 | The proximity of multiple CPU cores on the same die allows the cache coherency circuitry to operate at a much higher clock rate than what is possible if the signals have to travel off-chip. Combining equivalent CPUs on a single die significantly improves the performance of cache snoop operations. Put simply, this mean... |
3,067 | Assuming that the die can physically fit into the package, multi-core CPU designs require much less printed circuit board space than do multi-chip SMP designs. Also, a dual-core processor uses slightly less power than two coupled single-core processors, principally because of the decreased power required to drive sign... |
3,068 | Multi-core chips also allow higher performance at lower energy. This can be a big factor in mobile devices that operate on batteries. Since each core in a multi-core CPU is generally more energy-efficient, the chip becomes more efficient than having a single large monolithic core. This allows higher performance with le... |
3,069 | Maximizing the usage of the computing resources provided by multi-core processors requires adjustments both to the operating system support and to existing application software. Also, the ability of multi-core processors to increase application performance depends on the use of multiple threads within applications. |
3,070 | Integration of a multi-core chip can lower the chip production yields. They are also more difficult to manage thermally than lower-density single-core designs. Intel has partially countered this first problem by creating its quad-core designs by combining two dual-core ones on a single die with a unified cache, hence a... |
3,071 | The trend in processor development has been towards an ever-increasing number of cores, as processors with hundreds or even thousands of cores become theoretically possible. In addition, multi-core chips mixed with simultaneous multithreading, memory-on-chip, and special-purpose "heterogeneous" cores promise further p... |
3,072 | Chips designed from the outset for a large number of cores are sometimes referred to as manycore designs, emphasising qualitative differences. |
3,073 | The composition and balance of the cores in multi-core architecture show great variety. Some architectures use one core design repeated consistently , while others use a mixture of different cores, each optimized for a different, "heterogeneous" role. |
3,074 | How multiple cores are implemented and integrated significantly affects both the developer's programming skills and the consumer's expectations of apps and interactivity versus the device. A device advertised as being octa-core will only have independent cores if advertised as True Octa-core, or similar styling, as opp... |
3,075 | The article "CPU designers debate multi-core future" by Rick Merritt, EE Times 2008, includes these comments: |
3,076 | Atsushi Hasegawa, a senior chief engineer at Renesas, generally agreed. He suggested the cellphone's use of many specialty cores working in concert is a good model for future multi-core designs. |
3,077 | Anant Agarwal, founder and chief executive of startup Tilera, took the opposing view. He said multi-core chips need to be homogeneous collections of general-purpose cores to keep the software model simple. |
3,078 | An outdated version of an anti-virus application may create a new thread for a scan process, while its GUI thread waits for commands from the user . In such cases, a multi-core architecture is of little benefit for the application itself due to the single thread doing all the heavy lifting and the inability to balance ... |
3,079 | Given the increasing emphasis on multi-core chip design, stemming from the grave thermal and power consumption problems posed by any further significant increase in processor clock speeds, the extent to which software can be multithreaded to take advantage of these new chips is likely to be the single greatest constrai... |
3,080 | The telecommunications market had been one of the first that needed a new design of parallel datapath packet processing because there was a very quick adoption of these multiple-core processors for the datapath and the control plane. These MPUs are going to replace the traditional Network Processors that were based on ... |
3,081 | Parallel programming techniques can benefit from multiple cores directly. Some existing parallel programming models such as Cilk Plus, OpenMP, OpenHMPP, FastFlow, Skandium, MPI, and Erlang can be used on multi-core platforms. Intel introduced a new abstraction for C++ parallelism called TBB. Other research efforts incl... |
3,082 | Multi-core processing has also affected the ability of modern computational software development. Developers programming in newer languages might find that their modern languages do not support multi-core functionality. This then requires the use of numerical libraries to access code written in languages like C and For... |
3,083 | Managing concurrency acquires a central role in developing parallel applications. The basic steps in designing parallel applications are: |
3,084 | On the other hand, on the server side, multi-core processors are ideal because they allow many users to connect to a site simultaneously and have independent threads of execution. This allows for Web servers and application servers that have much better throughput. |
3,085 | Vendors may license some software "per processor". This can give rise to ambiguity, because a "processor" may consist either of a single core or of a combination of cores. |
3,086 | Embedded computing operates in an area of processor technology distinct from that of "mainstream" PCs. The same technological drives towards multi-core apply here too. Indeed, in many cases the application is a "natural" fit for multi-core technologies, if the task can easily be partitioned between the different proces... |
3,087 | In addition, embedded software is typically developed for a specific hardware release, making issues of software portability, legacy code or supporting independent developers less critical than is the case for PC or enterprise computing. As a result, it is easier for developers to adopt new technologies and as a result... |
3,088 | As of 2010, multi-core network processors have become mainstream, with companies such as Freescale Semiconductor, Cavium Networks, Wintegra and Broadcom all manufacturing products with eight processors. For the system developer, a key challenge is how to exploit all the cores in these devices to achieve maximum network... |
3,089 | In digital signal processing the same trend applies: Texas Instruments has the three-core TMS320C6488 and four-core TMS320C5441, Freescale the four-core MSC8144 and six-core MSC8156 . Newer entries include the Storm-1 family from Stream Processors, Inc with 40 and 80 general purpose ALUs per chip, all programmable in C... |
3,090 | In heterogeneous computing, where a system uses more than one kind of processor or cores, multi-core solutions are becoming more common: Xilinx Zynq UltraScale+ MPSoC has a quad-core ARM Cortex-A53 and dual-core ARM Cortex-R5. Software solutions such as OpenAMP are being used to help with inter-processor communication. |
3,091 | Mobile devices may use the ARM big.LITTLE architecture. |
3,092 | The research and development of multicore processors often compares many options, and benchmarks are developed to help such evaluations. Existing benchmarks include SPLASH-2, PARSEC, and COSMIC for heterogeneous systems. |
3,093 | ^ Digital signal processors have used multi-core architectures for much longer than high-end general-purpose processors. A typical example of a DSP-specific implementation would be a combination of a RISC CPU and a DSP MPU. This allows for the design of products that require a general-purpose processor for user inter... |
3,094 | ^ Two types of operating systems are able to use a dual-CPU multiprocessor: partitioned multiprocessing and symmetric multiprocessing . In a partitioned architecture, each CPU boots into separate segments of physical memory and operate independently; in an SMP OS, processors work in a shared space, executing threads w... |
3,095 | Multiprocessing is the use of two or more central processing units within a single computer system. The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There are many variations on this basic theme, and the definition of multiprocessing can ... |
3,096 | According to some on-line dictionaries, a multiprocessor is a computer system having two or more processing units each sharing main memory and peripherals, in order to simultaneously process programs. A 2009 textbook defined multiprocessor system similarly, but noting that the processors may share "some or all of the ... |
3,097 | At the operating system level, multiprocessing is sometimes used to refer to the execution of multiple concurrent processes in a system, with each process running on a separate CPU or core, as opposed to a single process at any one instant. When used with this definition, multiprocessing is sometimes contrasted with mu... |
3,098 | In Flynn's taxonomy, multiprocessors as defined above are MIMD machines. As the term "multiprocessor" normally refers to tightly coupled systems in which all processors share memory, multiprocessors are not the entire class of MIMD machines, which also contains message passing multicomputer systems. |
3,099 | In a multiprocessing system, all CPUs may be equal, or some may be reserved for special purposes. A combination of hardware and operating system software design considerations determine the symmetry in a given system. For example, hardware or software considerations may require that only one particular CPU respond t... |
3,100 | Systems that treat all CPUs equally are called symmetric multiprocessing systems. In systems where all CPUs are not equal, system resources may be divided in a number of ways, including asymmetric multiprocessing , non-uniform memory access multiprocessing, and clustered multiprocessing. |
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