Vector processor

For this computer system, the crossover point where direct SCF beats the conventional algorithm happens at around 120 basis functions ( N=7). This level may be lower for some vector processors. ... 

The computer time required for ab initio calculations is roughly proportional to the fourth power of the number of atomic basis functions used for the description of the molecular system. Ab initio calculations are thus not feasible today for host-guest systems with more than about 150—200 electrons. Supercomputers and vector processors will significantly lower the necessary CPU times150) but they alone probably cannot bring a breakthrough for systems larger than two or three times the ones which can be treated today. 

Perhaps the first question to be considered in contemplating the use of a vector processor in Quantum Chemistry (QC) is just how much advantage is obtainable with the minimum amount of effort i.e. by simply implementing software from a scalar machine with little or no modification. The answer to this question is readily obtainable by benchmarking the machine against some standard on a variety of widely used QC packages. Such an exercise would shed... 

GUEST AND WILSON Vector Processors in Quantum Chemistry... 

It is clear that we have dedicated a large amount of core in order to vectorise the code, and it is probable that many algorithms share this attribute. In general it is apparent that to drive a vector processor efficiently will require a large amount of store. 

With the advent of vector processors over the last ten years, the vector computer has become the most efficient and in some instances the only affordable way to solve certain computational problems. One such computer, the Texas Instruments Advanced Scientific Computer (ASC), has been used extensively at the Naval Research Laboratory to model atmospheric and combustion processes, dynamics of laser implosions, and other plasma physics problems. Furthermore, vectorization is achieved in these programs using standard Fortran. This paper will describe some of the hardware and software differences which distinguish the ASC from the more conventional scalar computer and review some of the fundamental principles behind vector program design. 

The Use of a High-Speed Vector Processor Machine for Chemical Kinetic Sensitivity Analysis... 

As a result of the transfer of the GF Method of sensitivity analysis to the vector machine, an improvement of more than a factor of 100 in running time has been achieved, with an associated cost effectiveness of about 60 from Scheme I on the Honeywell to Scheme II on the Cray. This has been accomplished not only by virtue of the use of a higher speed machine and the vector processor, but also by making the proper choice among alternative algorithms and paying close attention to coding details. 

Assuming that a reader of this book is more interested in vector processors, decision trees and differential equations than in organic chemistry, I will provide only some examples which are intended to clarify the foregoing discussion.(10) Figures 1 and 2 show some typical results of the program. 

A Micro Vector Processor for Molecular Mechanics Calculations... 

Figure 6. Logic diagram of the MVP-9500/8 vector processor card for S-100 bus...

The remaining obstacle to producing a working vector processor system is the library of FORTRAN callable subroutines. 

Figure 7. Block diagram of the MVP-9500/Vector MZ vector processor microcomputer system.

The estimated full commercial cost of an MVP-9500/8 system based on a Vector MZ with 5M bytes of disk space, printer and terminal is around 10,400, compared with around 25,000 for a PDP11/34 with similar peripherals and a floating point processor. This makes the vector processor option around eight times more cost effective than the PDP-11 PROVIDED THAT THE CALCULATION UNDER CONSIDERATION CAN MAKE EFFICIENT USE OF A VECTOR PROCESSOR. A similar comparison of the MVP-9500/128 and AP120B puts the former ahead by a factor of two in cost effectiveness. 

The primary reason for undertaking this whole exercise was to evaluate vector processors for use in molecular mechanics calculations and as an adjunct to chemical computer graphics systems ... 

Picture transformations (e.g. rotation, translation, scaling, perspective etc) in interactive computer graphics lend themselves naturally to representation in matrix notation, and implementation of the various algorithms on a vector processor is obviously straightforward and very worthwhile (particularly if moving pictures are required.). For this reason graphical applications of the MVP-9500 will not be discussed here and the interested reader is referred to one of the standard texts in this area (7). 

The author has presented details of a cost effective vector processor for use with S-100 microcomputers and produced a library of FORTRAN callable subroutines for general purpose floating point computations. Brief details of the construction of a molecular mechanics program using the vector processor have been given. 

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