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Solving the 1D Bin Packing Problem Using a Parallel Genetic Algorithm: A Benchmark Test
The past few decades have witnessed the introduction in a wide range of technological innovations that have had an enormous impact on consumers, businesses and governmental agencies. Computer-based applications in particular have been key in facilitating the delivery of a wide range of services and information, and computer processing speeds have consistently increased incrementally. Computer processing speeds, though, have a natural limit, with electricity being unable to travel faster than the speed of light. Therefore, even the optimal processing speeds attainable in the future will remain constrained in this regard, but there are some alternative approaches to computer processing that can further increase the functionality of computers, including parallel computing and genetic algorithms which are discussed further below.
In computing, the term "parallelism" is used to describe a system's architecture, in other words, "The organization and interconnection of components of computer systems" (Faulkner, Senker & Velho, 1999, p. 135). Although processing speeds have continued to double roughly every 18 months following Moore's Law, computers that use sequential architectures are still constrained in several ways in their ability to perform calculation functions. Irrespective of how fast a computer functions in sequential architectural configurations, each separate instruction or processing operation must be completed prior to the initiation of the next instruction or processing operation (Faulkner et al., 1999). Clearly, increases in processing speed can help sequential processing function more efficiently, but even here there is a fundamental constraint. As Faulkner and his associates emphasize, "This approach has its barriers, not least the speed of light since electrical signals cannot travel faster than light. Another way to increase the performance of computers is to find an alternative architecture" (Faulkner et al., 1999, p. 135). In response to the need for faster and more efficient computer processing, a number of devices have been introduced during the past half century or so that have employed numerous processors that operate in parallel to accomplish a single task (Faulker et al., 1999). According to Faulkner and his associates, "Most of this development has involved the gradual introduction of parallelism into supercomputers. There are six main forms: concurrent input -- output, operations, pipelining, memory interleaving and hierarchy, parallel functional units, vector processing, and multiple central processors. However, none of these approaches completely abandons the sequential architecture" (1999, p. 136).
Parallel systems are comprised of a number of processors, each of which assumes responsibility for completion of discrete portions of a processing job simultaneously. Although attempts to produce truly parallel processing began during the late 1960s, it was not until the 1980s that the approach became commercially viable with the introduction of so-called "field effect chips" (Faulkner et al., 1999). According to MacKenzie, "In field effect chips, current flows only in the surface plane of the microchip; in a bipolar chip, the current flow perpendicular to the chip as well as along it" (1998, p. 106). Based on its ability to be mass produced with relative ease, highly integrated field effect technology introduced a number of opportunities for configuring large numbers of field effect chips in parallel architectures (MacKenzie, 1998). As Faulkner and his colleagues point out, "Although slower than the bipolar chips conventionally used in supercomputers, large numbers of [field effect chips] could be arrayed or configured in highly parallel architectures to achieve competitive processing speeds" (1999, p. 137). Beginning in the 1980s, parallel architectures became increasingly competitive with so-called supercomputers. In this regard, MacKenzie notes that, "Until the very end of the 1980s, these did not claim to rival mainstream supercomputing in absolute floating-point performance, promising instead a superior price-performance ratio. However, by the start of the 1990s, with the most advanced field effect chips (such as the million-transistor Intel i1860) being claimed to offer on a single chip a floating-point processing performance approaching that of a 1976 Cray I, rivalry in absolute performance was growing" (1998, p. 107).
More recently, parallel computers have in fact started to compare favorably with the performance levels achieved by supercomputers through the use of incremental parallelism; however, the primary advantage from the start has been this increased price-performance ratio by reducing the costs that are associated with attaining the fastest processing speeds (Faulkner et al., 1999). Parallel computers differ from sequential processing methods in three basic ways that are related to their design as described in Table 1 below.
Basic differences between parallel and sequential processing
The type and number of processors, or the "granularity" that are used.
The majority of computers currently in use contain identical processors only; however, it is possible to conceive of heterogeneous machines working with different processors. The system may be either 'coarse-grain' -- composed of a small number of sophisticated processors -- or 'fine-grain' -- employing a large number of simple processors.
Parallel architectures vary in the kind of instruction given to the different processors.
Parallel-data computers, also known as single instruction stream/multiple data stream, have all the processors simultaneously executing the same operation on different parts of the data. Parallel-process computers, or multiple instruction stream/multiple data stream are able to divide large programs into many smaller ones that separate processors execute simultaneously.
Parallel computers differ in the way the processors are connected to one another and to the memory units.
In 'shared memory' machines, communications between the processors is via a common memory that is accessed through a network of connections or a memory bus. This approach is hampered by the occurrence of potential for 'traffic jams.' 'Distributed memory' machines have some amount of memory attached to each processor, forming the nodes or processor-memory pairs; communication is via a message-passing system. The problem here is how to connect the nodes so that communication between them is fast: no node has to support too many connections. Various geometries have been devised including the simple rectangular grid used by the DAP (distributed array processor) machine, developed in the UK, and specialized geometries such as the Butterfly computer and the n-cube or hypercube, both developed in the U.S. In the latter, the nodes are placed at the corners of a multidimensional cube whose edges correspond to the links between processors: in the sixteen processor architecture, for instance, each processor is linked to four other processors. A more advanced approach is now found in the British designed transputer, in which the connections between processors are 'virtual' rather than hardwired. The transputer is a microprocessor which 'can be used both as a building block for parallel processing machines and as a single very high performance microprocessor for computers and embedded applications. In principle, different geometries can be designed -- or (in the case of computers using transputers) reconfigured -- so as to 'match' the application problem to be solved.
Source: Faulkner et al., 1999, p. 138
It is important to note that parallel computing, though, is not a zero-sum alternative to sequential processing. In this regard, Benkler emphasizes that, "One must break up the problem into well-designed pieces that can run simultaneously, rather than having one processor wait for the other to finish, and there is overhead in managing the information input and output flows to and from the processors, both to each other and to the system memory" (2005, p. 273). The analysis of the performance-price ratio between parallel and sequential processing therefore requires an assessment of what benefits can be realized by integrating numerous separate processors compared to the costs that are involved in building these capacities into a single machine (Benkler, 2005). Because parallel processing offers some advantages over the "all-in-one" approach, the popularity of parallel processing has continued to increase in recent years. In this regard, Benkler concludes that, "By the end of the twentieth century, most supercomputers were made of thousands of simple processors lashed together and parallelization became an important field of computer science" (Benkler, 2005, p. 274). These trends in alternative processing approaches have been augmented by other innovations, including evolutionary computing which is discussed further below.
As the term suggests, evolutionary computing is founded on the same principles that Charles Darwin proposed in Origin of Species. For instance, Pennock notes that, "Computer scientists and engineers, inspired by the workings of evolution in nature, realized that they could apply the same powerful Darwinian mechanism in computers for practical purposes, such as for complex industrial design" (2007, p. 212). In recent years, evolutionary computing techniques have been used to develop algorithms for online decision making applications (Karr, 2007).
In fact, evolutionary computing has been used by the National Aeronautics and Space Administration (NASA) to good effect already by developing evolutionary algorithms that facilitate design and development. For example, a research team at NASA's Ames Research Center used evolutionary computing techniques to automatically create the design for an antenna for use on a satellite in earth orbit. According to Plotkin, "The space antenna, which looks like an unwound paper clip, violated conventional wisdom about antenna design and confounded the human antenna…[continue]
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