[petsc-users] Doubt on how to copy a Mat into another (Fortran)

[Marco Tiberga]

Dear Matt,

Thanks for your reply, now it’s clear to me also why matArray is not destroyed, contrarily to Amat.

Do you think that declaring explicitly matArray as a (Fortran) pointer (at line 113) and then using “matArray(1) => Amat” would be equivalent? It would be certainly clearer from the Fortran point of view.

With kind regards,
Marco Tiberga

From: Matthew Knepley [mailto:knepley at gmail.com]
Sent: maandag 4 februari 2019 17:46
To: Marco Tiberga
Cc: petsc-users at mcs.anl.gov; Aldo Hennink - TNW; Danny Lathouwers - TNW
Subject: Re: [petsc-users] Doubt on how to copy a Mat into another (Fortran)

On Mon, Feb 4, 2019 at 11:16 AM Marco Tiberga via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:
Dear PETSc developers,

Since I am learning how to use MatCreateNest, I was looking at example ex73f90t.F90<https://www.mcs.anl.gov/petsc/petsc-current/src/snes/examples/tutorials/ex73f90t.F90.html> (I am using Fortran).

At line 297, the array of matrices to be passed to MatCreateNest is initialized with code lines as “matArray(1) = Amat”.

That is a pointer. It does not create a replica in memory, as the calls below do. Fortran is not explicit about this distinction
which can lead to confusion.

  Thanks,

    Matt


I was surprised to find such a simple command, I thought a matrix copy should be done by a sequence like
“ call MatDuplicate(Amat, MAT_SHARE_NONZERO_PATTERN,matArray(1),ierr); CHKERRA(ierr)
  call MatCopy(Amat,matArray(1), SAME_NONZERO_PATTERN,ierr); CHKERRA(ierr) “

So, I was wondering: are the two ways completely equivalent, and therefore the second unnecessarily more complex? or is the latter more robust and therefore preferable?
Is there any difference in terms of performance?

Thanks a lot for the clarification.

Best regards,
Marco Tiberga
PhD candidate
Delft University of Technology
Faculty of Applied Sciences
Radiation Science & Technology Department
Mekelweg 15, 2629 JB Delft, The Netherlands
E-Mail: m.tiberga at tudelft.nl<mailto:m.tiberga at tudelft.nl>
Website: http://www.nera.rst.tudelft.nl/





--
What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
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https://www.cse.buffalo.edu/~knepley/<http://www.cse.buffalo.edu/~knepley/>
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