[petsc-users] Precision of MatView

[Sanjay Govindjee]

Problem resolved.

As I suspected the problem was mine.  My parallel runs were being 
performed using input files that has a lower precision in the input
data than those being used in my serial runs.

-sanjay


On 5/15/19 7:25 AM, Mark Adams wrote:
> 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 
> <mailto: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 <mailto: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 <mailto: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
>     <mailto: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
>     >>
>     >
>

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