[petsc-users] error: invalid types ‘PetscScalar* {aka double*}[PetscScalar {aka double}]’ for array subscript

[Matthew Knepley]

On Tue, Sep 1, 2020 at 1:16 AM Smit Thijs <thijs.smit at hest.ethz.ch> wrote:

> Hi Matt,
>
>
>
> Thanks for your replay.
>
>
>
> I am working with a structured grid and in this case the content of the
> vector to be mapped does not overlap between processes. My understanding
> (although I am a beginner with PETSc) is that I don’t have to use IS in
> that case?
>
>
>
>     ierr = DMCreateGlobalVector(da_elem, &xPhys);
>
>     CHKERRQ(ierr);
>
>
>
> Is there a way to solve this problem without using IS?
>

What I say below is that you cannot index a C array with a real number. You
have to do it with an integer. A PETSc IS is a list of integers, which is
why I suggested that.

  Thanks,

     Matt


> Best, Thijs
>
>
>
> *From:* Matthew Knepley <knepley at gmail.com>
> *Sent:* 21 August 2020 18:20
> *To:* Smit Thijs <thijs.smit at hest.ethz.ch>
> *Cc:* petsc-users at mcs.anl.gov
> *Subject:* Re: [petsc-users] error: invalid types ‘PetscScalar* {aka
> double*}[PetscScalar {aka double}]’ for array subscript
>
>
>
> On Fri, Aug 21, 2020 at 11:49 AM Smit Thijs <thijs.smit at hest.ethz.ch>
> wrote:
>
> Hi All,
>
>
>
> I am having the following error when I try to do a mapping with vectors
> and I can’t figure out how to solve this or what is going wrong:
>
> error: invalid types ‘PetscScalar* {aka double*}[PetscScalar {aka
> double}]’ for array subscript
>
>              xpMMA[i] = xp[indicesMap[i]];
>
>
>
> Herewith two code snippets:
>
>     // total number of elements on core
>
>     PetscInt nel;
>
>     VecGetLocalSize(xPhys, &nel);
>
>
>
>     // create xPassive vector
>
>     ierr = VecDuplicate(xPhys, &xPassive);
>
>     CHKERRQ(ierr);
>
>
>
>     // create mapping vector
>
>     ierr = VecDuplicate(xPhys, &indicator);
>
>     CHKERRQ(ierr);
>
>
>
>     // index set for xPassive and indicator
>
>     PetscScalar *xpPassive, *xpIndicator;
>
>     ierr = VecGetArray(xPassive, &xpPassive);
>
>     CHKERRQ(ierr);
>
>     ierr = VecGetArray(indicator, &xpIndicator);
>
>     CHKERRQ(ierr);
>
>
>
>     // counters for total and active elements on this processor
>
>     PetscInt tcount = 0; // total number of elements
>
>     PetscInt acount = 0; // number of active elements
>
>     PetscInt scount = 0; // number of solid elements
>
>     PetscInt rcount = 0; // number of rigid element
>
>
>
>     // loop over all elements and update xPassive from wrapper data
>
>     // count number of active elements, acount
>
>     // set indicator vector
>
>     for (PetscInt el = 0; el < nel; el++) {
>
>         if (data.xPassive_w.size() > 1) {
>
>             xpPassive[el] = data.xPassive_w[el];
>
>             tcount++;
>
>             if (xpPassive[el] < 0) {
>
>                 xpIndicator[acount] = el;
>
>                 acount++;
>
>             }
>
>         } else {
>
>             xpPassive[el] = -1.0; // default, if no xPassive_w than all
> elements are active = -1.0
>
>         }
>
>     }
>
>
>
>     // printing
>
>     //PetscPrintf(PETSC_COMM_WORLD, "tcount: %i\n", tcount);
>
>     //PetscPrintf(PETSC_COMM_WORLD, "acount: %i\n", acount);
>
>
>
>     // Allreduce, get number of active elements over all processes
>
>     // tmp number of var on proces
>
>     // acount total number of var sumed
>
>     PetscInt tmp = acount;
>
>     acount = 0.0;
>
>     MPI_Allreduce(&tmp, &(acount), 1, MPIU_INT, MPI_SUM, PETSC_COMM_WORLD);
>
>
>
>     //// create xMMA vector
>
> VecCreateMPI(PETSC_COMM_WORLD, tmp, acount, &xMMA);
>
>
>
>    // Pointers to the vectors
>
>     PetscScalar *xp, *xpMMA, *indicesMap;
>
>
>
> Here you declare indicesMap as PetscScalar[]. You cannot index an array
> with this. I see that you
>
> want to store these indices in a Vec. You should use an IS instead.
>
>
>
>   Thanks,
>
>
>
>      Matt
>
>
>
>     //PetscInt indicesMap;
>
>     ierr = VecGetArray(MMAVector, &xpMMA);
>
>     CHKERRQ(ierr);
>
>     ierr = VecGetArray(elementVector, &xp);
>
>     CHKERRQ(ierr);
>
>     // Index set
>
>     PetscInt nLocalVar;
>
>     VecGetLocalSize(xMMA, &nLocalVar);
>
>
>
>     // print number of var on pocessor
>
>     PetscPrintf(PETSC_COMM_WORLD, "Local var: %i\n", nLocalVar);
>
>
>
>     ierr = VecGetArray(indicator, &indicesMap);
>
>     CHKERRQ(ierr);
>
>
>
>     // Run through the indices
>
>     for (PetscInt i = 0; i < nLocalVar; i++) {
>
>         if (updateDirection > 0) {
>
>             //PetscPrintf(PETSC_COMM_WORLD, "i: %i, xp[%i] = %f\n", i,
> indicesMap[i], xp[indicesMap[i]]);
>
>             xpMMA[i] = xp[indicesMap[i]];
>
>         } else if (updateDirection < 0) {
>
>             xp[indicesMap[i]] = xpMMA[i];
>
>             //PetscPrintf(PETSC_COMM_WORLD, "i: %i, xp[%i] = %f\n", i,
> indicesMap[i], xp[indicesMap[i]]);
>
>         }
>
>     }
>
>     // Restore
>
>     ierr = VecRestoreArray(elementVector, &xp);
>
>     CHKERRQ(ierr);
>
>     ierr = VecRestoreArray(MMAVector, &xpMMA);
>
>     CHKERRQ(ierr);
>
>     ierr = VecRestoreArray(indicator, &indicesMap);
>
>     CHKERRQ(ierr);
>
>     PetscPrintf(PETSC_COMM_WORLD, "FINISHED UpdateVariables \n");
>
>
>
> The error message says that the type with which I try to index is wrong, I
> think. But VecGetArray only excepts scalars. Furthermore, the el variable
> is an int, but is seams like to turn out to be a scalar. Does anybody see
> how to proceed with this?
>
>
>
> Best regards,
>
>
>
> Thijs Smit
>
>
>
>
> --
>
> What most experimenters take for granted before they begin their
> experiments is infinitely more interesting than any results to which their
> experiments lead.
> -- Norbert Wiener
>
>
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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