[petsc-users] Rectangular matrix

[Jin, Shuangshuang]

Hello,

        I would like to ask if there's any special setup for PTESc to solve an Ax=b problem where A is a rectangular matrix instead of a square matrix. For example, when my A matrix is 3*3, the problem can be solved properly. But when my A matrix is 4*3, the error message is:

[0]PETSC ERROR: Arguments are incompatible!
[0]PETSC ERROR: Incompatible vector local lengths 4 != 3!

PS: I created the matrix in SeqAIJ format and I could view the matrix was constructed correctly by MatView.

  // determine number of nonzeros per row in the new matrix
  PetscMalloc((n+1)*sizeof(PetscInt),&cnt);
  for (i=0;i<n;i++) {
    cnt[i]=irow[i+1]-irow[i];
  }
  MatCreateSeqAIJ(PETSC_COMM_SELF,n,m,0,cnt,&A);
  MatSetOption(A,MAT_IGNORE_ZERO_ENTRIES,PETSC_TRUE);
  // copy over the matrix entries from the inputs
  for (i=0;i<n;i++) {
    PetscMalloc(cnt[i]*sizeof(PetscInt),&col);
    for (j=0;j<cnt[i];j++) {
      col[j]=icol[irow[i]+j-1]-1;
    }
    MatSetValues(A,1,&i,cnt[i],col,&ival[irow[i]-1],INSERT_VALUES);
  }
  MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
  MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
  ierr=PetscPrintf(PETSC_COMM_WORLD,"Matrix A:\n");CHKERRQ(ierr);
  MatView(A,PETSC_VIEWER_STDOUT_SELF);

        I'm new to PETSc. Sorry if my questions is naïve to you. But  any comment is highly appreciated!

Thanks,
Shuangshuang


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