User-difined PC

Matthew Knepley knepley at
Mon Sep 22 07:49:09 CDT 2008

On Mon, Sep 22, 2008 at 5:31 AM, Michel Cancelliere
<fernandez858 at> wrote:
> Hello,
> I have problems with the implementation of a user-defined pc, basically my
> program is in a cycle, for with which he is called by matlab each time it
> seeks to solve a linear system, the problem is that in the first iteration
> of the for-cycle  the preconditioner works very well, then fails to
> convergence. It may be some parameters that I setting wrong?
> I'am attaching my program code.

I cannot see anything wrong just by looking at the code. To test it, I
would send the
same matrix in multiple times and make sure that the convergence was the same.
If not, it should be easy to track back in the debugger to the first
different residual.


> Thank you,
> Michel
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener

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