[Octave-patch-tracker] [patch #9282] add minres for sparse linear systems

[Xie Rui]

Follow-up Comment #9, patch #9282 (project octave):

Hi Nicholas,

Thank you for the test.
In Comment #8, A is symmetric but not hermitian. I think we should test for
hermitian A as well. For example, I substituted A into the matlab example in
Comment #1.


n = 100; on = ones(n,1);
A = spdiags ([-2*on 4*on -2*on], -1:1, n, n);
b = sum(A,2); 
tol = 1e-10; 
maxit = 50; 
M1 = spdiags(4*on,0,n,n);

A = spdiags([(-2 - 2 * 1i)*on (4 + 4)*on (-2 + 2 * 1i)*on],-1:1,n,n); %I added
this line

x = minres(A,b,tol,maxit,M1);

% [x,flag,relres,iter,resvec] = minres(A,b,tol,maxit,M1); 
% use this if you want the full outputs.


I tried it with my minres. It converged after 26 iterations, and the relative
residual is  8.4181e-011. 
In addition, it failed to converge as for the test in comment #8.

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