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<DIV><FONT face=Verdana
size=2>>Date: Fri, 2 Dec 2011 08:07:54 -0600</DIV>
<DIV>
<DIV>>From: Jed Brown <jedbrown@mcs.anl.gov></DIV>
<DIV>>Subject: Re: [petsc-users] How to output the values of a parallel</DIV>
<DIV>>PETSc vector to a ASCII file</DIV>
<DIV>>To: PETSc users list <petsc-users@mcs.anl.gov></DIV>
<DIV>>Message-ID:</DIV>
<DIV><CAM9tzSkSeN3Z11vdadF66XTe_KVbUo-eA=2hvAgROFkTJfsYZg@mail.gmail.com></DIV>
<DIV>>Content-Type: text/plain; charset="utf-8"</DIV>
<DIV></DIV>
<DIV>>On Fri, Dec 2, 2011 at 08:04, Feng-Chao Wang <wolfshow@gmail.com> wrote:</DIV>
<DIV></DIV>
<DIV>> **</DIV>
<DIV>> Dear all,</DIV>
<DIV>></DIV>
<DIV>> I intend to postprocess the solution of a PDE (stored in a</DIV>
<DIV>> parallel PETSc vector ) using tecplot. Thus I want to output the values of</DIV>
<DIV>> the parallel vector as well as other data (such as the grid information) to</DIV>
<DIV>> a ASCII file.</DIV>
<DIV>></DIV>
<DIV>> When I deal this with</DIV>
<DIV>></DIV>
<DIV>> VecGetArray(U, &u);</DIV>
<DIV>></DIV>
<DIV>> for (i=0; i<Mx*My; i++)</DIV>
<DIV>> {</DIV>
<DIV>> PetscViewerASCIIPrintf(viewer,"%F %F %F", x, y, u[i]);</DIV>
<DIV>> }</DIV>
<DIV>></DIV>
<DIV>> If more than 1 processor are used, I found that only part of the value of</DIV>
<DIV>> u was output correctly (that stored on the first processor).</DIV>
<DIV>> I found in the manual page of "PetscViewerASCIIPrintf" that "Not</DIV>
<DIV>> Collective, but only first processor in set has any effect"</DIV>
<DIV>></DIV>
<DIV></DIV>
<DIV>>If you can afford the memory:</DIV>
<DIV></DIV>
<DIV>>http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Vec/VecScatterCreateToZero.html</DIV>
<DIV> </DIV>
<DIV>Thank you very much!</DIV>
<DIV>I tried the Scatter method. I found that even I scatter the parallel vector
to a sequential vector, when I want to output this sequential vector to the
file, I still can not use
"PetscViewerASCIIPrintf(viewer,"%F %F %F", x, y, u[i]);",
because the vector can not be directly accessed for output?</DIV>
<DIV> </DIV>
<DIV> Thus I used VecGetArray(U, &u); and then
PetscViewerASCIIPrintf. I still got part of the sequential vector, because the
array u is stored on all the processor?</DIV>
<DIV> </DIV>
<DIV>>Slower:</DIV>
<DIV></DIV>
<DIV>><A
href="http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Sys/PetscSynchronizedPrintf.html">http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Sys/PetscSynchronizedPrintf.html</A></DIV>
<DIV> </DIV>
<DIV>I tried the PetscSynchronizedPrintf and got the same result. As a beginner
of PETSc, I wonder if I can output the value of a vector U to the ASCII file
using Printf("%f", U[i])? </DIV>
<DIV>If so, I can get the result I want.</DIV>
<DIV> </DIV>
<DIV>Or, I must use VecGetArray(U, &u); before I want to access the
data stored in the vector?</DIV>
<DIV> </DIV>
<DIV>Thank you!</DIV>
<DIV> </DIV>
<DIV></DIV>
<DIV>>Binary output can be written in parallel using</DIV>
<DIV></DIV>
<DIV>><A
href="http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Vec/VecView.html">http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/Vec/VecView.html</A></DIV>
<DIV> </DIV>
<DIV>Yes, the VecView can output the correct data stored in the parallel vector
to a ASCII file. However, I want to output not only the vector value but also
the grid information according to the tecplot file format, for example, there
are three column of data in one file:</DIV>
<DIV> </DIV>
<DIV>x[0] y[0] vec_value[0]</DIV>
<DIV>x[1] y[1] vec_value[1]</DIV>
<DIV>x[2] y[2] vec_value[2]</DIV>
<DIV>x[3] y[3] vec_value[3]</DIV>
<DIV>x[4] y[4] vec_value[4]</DIV>
<DIV>x[5] y[5] vec_value[5]</DIV>
<DIV>... ... ...</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>******************************************</DIV></FONT></DIV></BODY></HTML>