[petsc-users] Precision of MatView

[Mark Adams]

This thread suggests that I was at least not wrong in assuming that
trailing 0s should be printed by printf (although I did not trace the code
down to printf)

https://stackoverflow.com/questions/277772/avoid-trailing-zeroes-in-printf

Maybe Sanjay's machines printf cuts off trailing 0s.

On Wed, May 15, 2019 at 10:06 AM Smith, Barry F. <bsmith at mcs.anl.gov> wrote:

>
>    The 10-20% in seven digits are presumably printed accurately; it is
> presumably simply the case that the rest of the digits would be zero and
> hence are not printed.
>
> > On May 15, 2019, at 8:59 AM, Mark Adams via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> >
> > You are seeing half precision (like 7 digits) in 10-20% of the entries
> and full in the rest.
> >
> > Someone will probably chime in who knows about this but I can see where
> a serial matrix is printed in ASCII Matlab in MatView_SeqAIJ_ASCII in
> src/mat/impls/aij/seq/aij.c.
> >
> > I think this line is operative and is should clearly work:
> >
> >         ierr = PetscViewerASCIIPrintf(viewer,"%D %D
> %18.16e\n",i+1,a->j[j]+1,(double)a->a[j]);CHKERRQ(ierr);
> >
> > Could you run in serial (this code could very well be used for MPI Mats
> also) with Matlab/ASCII to verify that you have this problem. And you could
> modify this print statement and remake PETSc, if that's easy, to verify
> that this code is operative.
> >
> > I think %18.16e should print 16 digits even if they are 0s ...
> >
> >
> > On Tue, May 14, 2019 at 8:34 PM Sanjay Govindjee <s_g at berkeley.edu>
> wrote:
> > I'm seeing half precision on at least 10 to 20% of the entries :(
> > Knowing I should see full precision, I will dig deeper.
> >
> > -sanjay
> > On 5/14/19 5:22 PM, Mark Adams wrote:
> >> I would hope you get full precision. How many digits are you seeing?
> >>
> >> On Tue, May 14, 2019 at 7:15 PM Sanjay Govindjee via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> >> I am using the following bit of code to debug a matrix.  What is the
> >> expected precision of the numbers that I will find in my ASCII file?
> >> As far as I can tell it is not the full double precision that I was
> >> expecting.
> >>
> >>              call PetscViewerASCIIOpen(PETSC_COMM_WORLD,
> >> tangview,K_view, ierr)
> >>              call PetscViewerSetFormat(K_view,
> >> PETSC_VIEWER_ASCII_MATLAB, ierr)
> >>              call MatView                     (Kmat, K_view, ierr)
> >>
> >> -sanjay
> >>
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20190515/4ac2e9aa/attachment.html>