Programming methodologies

Basically, there are three possible methods by which we could perform the numerical calculations which we are going to encouter during this course.

Firstly, we could use a mathematical software package, such as MATHEMATICA¹, MAPLE²or MATLAB.³ The main advantage of these packages is that they facilitate the very rapid coding up of numerical problems. The main disadvantage is that they produce executable code which is interpreted, rather than compiled. Compiled code is translated directly from a high-level language into machine code instructions, which, by definition, are platform dependent--after all, an Intel x86 chip has a completely different instruction set to a Power-PC chip. Interpreted code is translated from a high-level language into a set of meta-code instructions which are platform independent. Each meta-code instruction is then translated into a fixed set of machine code instructions which is peculiar to the particular hardware platform on which the code is being run. In general, interpreted code is nowhere near as efficient, in terms of computer resource utilization, as compiled code: i.e., interpreted code run a lot slower than equivalent compiled code. Thus, although MATHEMATICA, MAPLE, and MATLAB are ideal environments in which to perform relatively small calculations, they are not suitable for full-blown research projects, since the code which they produce generally runs far too slowly.

Secondly, we could write our own programs in a high-level language, but use calls to pre-written, pre-compiled routines in commonly available subroutine libraries, such as NAG,⁴ LINPACK,⁵ and ODEPACK,⁶ to perform all of the real numerical work. This is the approach used by the majority of research physicists.

Thirdly, we could write our own programs--completely from scratch--in a high-level language. This is the approach used in this course. I have opted not to use pre-written subroutine libraries, simply because I want students to develop the ability to think for themselves about scientific programming and numerical techniques. Students should, however, realize that, in many cases, pre-written library routines offer solutions to numerical problems which are pretty hard to improve upon.