[GAP Forum] Another memory problem

mim_ at op.pl mim_ at op.pl
Fri Mar 14 09:02:04 GMT 2008


I am using Deriviations function to calculate Lie Algebra of derivations of some algebra created from octonions. I have noticed that Derivations works up to 36-dimension algebra. If the original algebra is bigger dimension there is memory problem and GAP quits.
I have looked into the Derivations function in lib/alglie.gi file. The matrix 
A:= NullMat( n^2, n^3, R ); is created and this is the reason of the memory problem.

I start GAP with option -m 300m. If I try bigger value I see following error:

  D:\gap4r4\bin>D:\GAP4R4\bin\gapw95.exe -m 400m -o 3000m -g -l D:\GAP4R4\
  gap: cannot extend the workspace any more
  gap: Press <Enter> to end program

So it looks I can only use 300MB of memory for GAP. But I have 1.5GB memory in my laptop. I can also define paging file which should be used as memory. I am using Windows XP Professional, processor Intel 1.7Ghz, IBM laptop R52.

Example of error in Derivations:
A:=MatrixAlgebra(Rationals, 6);     ba:=Basis(A);     DA:=Derivations(ba);
Error is shown:
gap: cannot extend the workspace any more
gap: Press <Enter> to end program

I have following questions
1. Why I can only start GAP with -m 300m option ?
2. How to test how much memory given matrix A is using in GAP ?
3. Has anybody tried to overwrite Derivations function to use smaller matrices ? E.g. we could declare smaller matrices NullMat( n^2, n^2, R ) in loop and solve partially equation via NullspaceMatDestructive(). Finally build intersection space for the result.

Marek Mitros

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