[Octave-bug-tracker] [bug #32804] Memory leak solving linear system (left division "\") with sparse matrix

[Paolo G. Ferrandi]

URL:
  <http://savannah.gnu.org/bugs/?32804>

                 Summary: Memory leak solving linear system (left division
"\") with sparse matrix
                 Project: GNU Octave
            Submitted by: paolo
            Submitted on: Wed 16 Mar 2011 11:31:51 AM GMT
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 3.2.4
        Operating System: GNU/Linux

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Details:

A massive memory allocation is caused by the following code. The allocated
memory is never freed until you quit GNU Octave.


nx=1000;
K=spdiags ([-ones(nx+1,1), 2*ones(nx+1,1), ...
           -ones(nx+1,1)],-1:1,nx+1,nx+1);
[L,U]=lu (K);
b=ones (1001,1);
for t=1:1e6
        y=L\b;
end


lu returns L as a permuted-lower sparse matrix. Since L is a lower matrix, you
can change matrix type to lower:


nx=1000;
K=spdiags ([-ones(nx+1,1), 2*ones(nx+1,1), ...
           -ones(nx+1,1)],-1:1,nx+1,nx+1);
[L,U]=lu (K);
L=matrix_type (L,'lower');
b=ones (1001,1);
for t=1:1e6
        y=L\b;
end


In the latter case there is not any massive memory allocation  and everything
seems to be fine.

Paolo






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