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memory problem

From: John W. Eaton
Subject: memory problem
Date: Wed, 2 Feb 2000 04:24:17 -0600 (CST)

On  1-Feb-2000, Daniel Heiserer <address@hidden> wrote:

| The machine has sufficient memory to process my request.

Apparently not. :-(

How much virtual memory do you have?

| octave:2> tic;eval(sprintf("L_%08d=eye(1000);",[1:1000]));toc
| error: memory exhausted -- trying to return to prompt
| .........
|  wd   matrix             1000   1000  L_00000232
|  wd   matrix             1000   1000  L_00000233
| ==> octave could create only 233 matrizes.

That's about 233 * 1000 * 1000 * 8 ==> 1.8GB of data (unfortunately,
even though eye produces a diagonal matrix, Octave currently uses a
full matrix to store it).

| In matlab it works fine. See below.
| I had an experience with fortran before, 
| where I had a memory limitation inside
| a subroutine, but defining everything as 
| a common block it worked. Maybe that is
| a hint ..........
| matlab:
| >> tic;eval(sprintf('L_%08d=eye(1000);',[1:1000]));toc
| elapsed_time =
|    72.8044
| ...................
|   L_00000999    1000x1000     8000000  double array
|   L_00001000    1000x1000     8000000  double array
| Grand total is 1000000000 elements using 8000000000 bytes

Thats about 8GB of data.  Do you really have that much virtual memory
available?  If not, I'd guess that Matlab is actually using a smarter
storage scheme (either storing only the diagonal, or even just
recognizing an identity matrix as special, or recognizing that it
really only needs data for one 1000x1000 identity matrix that can be
shared among all your identifiers).

What happens if you replace eye() with rand()?  Do you still have
enough memory to do this operation?


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