[Octave-bug-tracker] [bug #53258] test pcg.m fail

[Carlo de Falco]

Follow-up Comment #13, bug #53258 (project octave):

@Rik, If the correct default value was documented incorrectly I agree the docs
should be fixed, but I don't think the default value matters here as it was
already overridden to be N+1, right?

As for the number of iterations, if I recall correctly, pcg should produce the
exact solution after N iterations (and definitely that should be the case for
a diagonal matrix), N+1 was probably used to allow the algorithm to detect
convergence (as the test is performed at the beginning of the iteration) and
to set the flag accordingly.

Cristiano and/or Marco can you comment on why 2*N iterations seem to be needed
to robustly guarantee convergence?

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