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[Octave-bug-tracker] [bug #53140] Solution of a system of linear equatio

From: John W. Eaton
Subject: [Octave-bug-tracker] [bug #53140] Solution of a system of linear equations takes forever and hurts OS performance.
Date: Tue, 13 Feb 2018 17:11:10 -0500 (EST)
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0

Follow-up Comment #4, bug #53140 (project octave):

I changed the test script to be

load linsolve_test.mat;

disp ('leftdiv');
tic; x = A \ b; toc;
disp ('lu factorization');
tic; [L, U, P, Q, R] = lu (A); toc;
disp ('lu solve');
tic; xlu = Q * ( U \ ( L \ ( P * ( R \ b ) ) ) ); toc;

On my system, the two results are nearly identical (magnitude of max
difference is around 1e-20).  X has 3 more nonzero entries than XLU, but their
absolute values are all around 1e-22.

Performance is significantly different.  About 75 seconds for the leftdiv
operator and 20 seconds combined for the lu factorization and solve steps. 
Again, if someone is interested in digging into this, the place to start is


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