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Frank Leonard writes:

I have been attempting some constuctions of finite groups in GAP as

defined by a presentation in abstract generators/relators.

The problem consists of applying a certain algorithim to constuct a

group which I then attempt to identify. I also have access to the C.A.

package CAYLEY and have re-written the algorithim for CAYLEY. I have

found CAYLEY to be vastly superior (time wise) to GAP for this problem.

I assume that the fact that GAP programs/functions are interpreted

would be significant in explaining the performance discrepancies but I

am curious if there are any other factors which might be significant.

Can you tell me if there are any plans at present to write a compiler

for GAP?

I am sorry that we cannot really answer such an unspecified (but

nevertheless very critical) letter, much as we try to react to

criticism brought to our attention in the GAP-forum (or otherwise).

Frank Leonard has not told us what kind of problem he is really

looking at, nor which GAP functions he has used, nor even which

version of GAP.

There are of course functions for which the fact that they are

interpreted rather than originally written in C and compiled mean a

loss of efficiency. We know that this can in particular be the case

with functions which deal in a rather combinatorial way with small

data, as is the case with many functions handling presentations. For

this reason some of the functions for dealing with presentations have

parts in the kernel to circumvent this difficulty. If the

interpretation of GAP functions was the reason for inefficiency that

Frank Leonard has observed then it would be helpful for us to know,

*how* big the loss of efficiency was in his case for which functions,

e.g. in comparison with CAYLEY. It is not helpful just to be told

that CAYLEY was *vastly* superior for some function(s?) that are not

named applying "a certain algorithm" that he does not care to tell us

about.

It is also likely that for certain functions we are using genuinly

worse methods than CAYLEY (for others we may use better ones). Then we

want to know even more where this is the case in order to be able to

improve them.

We are not only open to but ask for constructive or at least well

specified criticism, but I must say that a letter like that of Frank

Leonard is not only unhelpful but rather discouraging.

Joachim Neubueser

PS. I have said already in a previous letter to the GAP-forum that the

idea to develop a compiler for GAP is being considered, but that, if

at all, a compiler cannot be expected in the nearer foreseeable

future.

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