[Octave-bug-tracker] [bug #63860] bicg fails with flag=2 starting with version 7.1.0

[Johannes]

URL:
  <https://savannah.gnu.org/bugs/?63860>

                 Summary: bicg fails with flag=2 starting with version 7.1.0
                   Group: GNU Octave
               Submitter: johannes
               Submitted: Thu 02 Mar 2023 10:16:44 AM UTC
                Category: Octave Function
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Regression
                  Status: None
             Assigned to: None
         Originator Name: Johannes
        Originator Email: 
             Open/Closed: Open
                 Release: 7.1.0
         Discussion Lock: Any
        Operating System: Any
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


-------------------------------------------------------
Date: Thu 02 Mar 2023 10:16:44 AM UTC By: Johannes <johannes>
The following code worked until 6.4.0:

Afn = @(x, type, qdyn) Amat(x, type, qdyn, Qlh, Shl);
for n = 1 : nconf
    qdyn  = cmp.aero.config.qdyn(n);
    u0    = qdyn * uQ(:, n);
    [disp(dofl, n), flag, ~, niter] = ...
         bicg(Afn, u0, opts.tol, opts.maxit, [], [],
              u0, qdyn);
    ...
end

It fails in 7.1.0 and higher versions returning flag=2. The reason is the
anonymous function for the preconditioners built by  __alltohandles__.m if no
preconditioner is supplied. It always has two input arguments, but the bigc
code also supplies the parameters, in this case qdyn, so there are three input
arguments.

A workaround is to modify the code as follows:

Afn = @(x, type, qdyn) Amat(x, type, qdyn, Qlh, Shl);
idn = @(x, y, z) x;  % avoid bug in 7.1.0
for n = 1 : nconf
    qdyn  = cmp.aero.config.qdyn(n);
    u0    = qdyn * uQ(:, n);
    [disp(dofl, n), flag, ~, niter] = ...
         bicg(Afn, u0, opts.tol, opts.maxit, idn, idn,
              u0, qdyn);
   ...
end









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