[petsc-users] Index set with zero size

[Tim Kroeger]

On Tue, 9 Nov 2010, Jed Brown wrote:

> On Tue, Nov 9, 2010 at 12:56, Tim Kroeger <tim.kroeger at cevis.uni-bremen.de> wrote:
>       Thank you, I found it now: The shell matrix does not implement MatMultAdd, only MatMult.  Of course, it
>       can't work then.  Thank you very much!
> 
> 
> Okay, but then it will error instead of silently modifying the vector.

It didn't.  And I did not forget CHKERRABORT() after the call to 
MatMultAdd().

Also, implementing MatMultAdd() for the shell did not resolve the 
problem.

I had a look into src/mat/impls/submat/submat.c (of petsc-3.1-p4) and 
found that MatMultAdd_SubMatrix() internally calls MatMult() (line 
155), not MatMultAdd().  Later in that method, some VecAYPX() is 
called (line 159), which might do the required addition.  Can you 
please confirm whether

(a) this is correct but explains why leaving MatMultAdd() of the shell 
undefined does not error; or

(b) everything remains as you said before; or

(c) this is a bug in that PETSc version?

Best Regards,

Tim

-- 
Dr. Tim Kroeger
CeVis -- Center of Complex Systems and Visualization
University of Bremen              tim.kroeger at cevis.uni-bremen.de
Universitaetsallee 29             tim.kroeger at mevis.fraunhofer.de
D-28359 Bremen                             Phone +49-421-218-7710
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