[petsc-users] MatMult() returning different values depending on # of processors?

[Arthur Kurlej]

I cannot send the original code, but I reproduced the problem in another
code. I have attached a makefile the code, and the data for the x vector
and A matrix.

I think the problem may be with my ShortenMatrix function, but it's not
clear to me what exactly is going wrong and how to fix it. So I would
appreciate some assistance there.


Thanks,
Arthur



On Wed, Jun 25, 2014 at 6:24 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>    Can you send the code that reproduces this behavior?
>
>    Barry
>
> On Jun 25, 2014, at 4:37 PM, Arthur Kurlej <akurlej at gmail.com> wrote:
>
> > Hi Barry,
> >
> > So for the matrix C that I am currently testing (size 162x162), the
> condition number is roughly 10^4.
> >
> > For reference, I'm porting MATLAB code into PETSc, and for one
> processor, the PETSc b vector is roughly equivalent to the MATLAB b vector.
> So I know that for one processor, my program is performing as expected.
> >
> > I've included examples below of values for b (also of size 162), ranging
> from indices 131 to 141.
> >
> > #processors=1:
> >                          0
> >      1.315217173959314e-20
> >      1.315217173959314e-20
> >      4.843201487740107e-17
> >      4.843201487740107e-17
> >      8.166104700666665e-14
> >      8.166104700666665e-14
> >      6.303834267553249e-11
> >      6.303834267553249e-11
> >      2.227932688485483e-08
> >      2.227932688485483e-08
> >
> > # processors=2:
> >      5.480410831461926e-22
> >      2.892553944350444e-22
> >      2.892553944350444e-22
> >      7.524038923310717e-24
> >      7.524038923214420e-24
> >     -3.340766769043093e-26
> >     -7.558372155761972e-27
> >      5.551561288838557e-25
> >      5.550551546879874e-25
> >     -1.579397982093437e-22
> >      2.655766754178065e-22
> >
> > # processors = 4:
> >      5.480410831461926e-22
> >      2.892553944351728e-22
> >      2.892553944351728e-22
> >      7.524092205125593e-24
> >      7.524092205125593e-24
> >     -2.584939414228212e-26
> >     -2.584939414228212e-26
> >                          0
> >                          0
> >     -1.245940797657998e-23
> >     -1.245940797657998e-23
> >
> > # processors = 8:
> >      5.480410831461926e-22
> >      2.892553944023035e-22
> >      2.892553944023035e-22
> >      7.524065744581494e-24
> >      7.524065744581494e-24
> >     -2.250265175188197e-26
> >     -2.250265175188197e-26
> >     -6.543127892265160e-26
> >     1.544288143499193e-317
> >      8.788794008375919e-25
> >      8.788794008375919e-25
> >
> >
> > Thanks,
> > Arthur
> >
> >
> >
> > On Wed, Jun 25, 2014 at 4:06 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >    How different are the values in b? Can you send back a few examples
> of the different b’s? Any idea of the condition number of C?
> >
> >    Barry
> >
> > On Jun 25, 2014, at 3:10 PM, Arthur Kurlej <akurlej at gmail.com> wrote:
> >
> > > Hi all,
> > >
> > > While running my code, I have found that MatMult() returns different
> values depending on the number of processors I use (and there is quite the
> variance in the values).
> > >
> > > The setup of my code is as follows (I can go into more
> depth/background if needed):
> > > -Generate parallel AIJ matrix of size NxN, denoted as A
> > > -Retrieve parallel AIJ submatrix from the last N-1 rows&columns from
> A, denoted as C
> > > -Generate vector of length N-1, denoted as x
> > > -Find C*x=b
> > >
> > > I have already checked that A, C, and x are all equivalent when ran
> for any number of processors, it is only the values of vector b that varies.
> > >
> > > Does anyone have an idea about what's going on?
> > >
> > >
> > > Thanks,
> > > Arthur
> > >
> >
> >
>
>
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