# [petsc-users] Corrrect usage of MatMumpsGetInverse()

Zhang, Hong hzhang at mcs.anl.gov
Mon Dec 16 15:57:17 CST 2019

```Jan:
You found a bug in our interface. I pushed a fix https://gitlab.com/petsc/petsc/commit/6fa4709e1488f7c58b0a4ecbdf34b75ae4ac64d2
in branch hzhang/fix-mumps-GetInverse.
You may give it a try by 'git checkout hzhang/fix-mumps-GetInverse' at PETSC_DIR and rebuild petsc.
Let me know if it fixes the issue.
Hong

Hello, everybody,
I am using PETSc version 3.12 together with MUMPS to calculate a part of an inverse from a matrix A.  For this I used the example mat/examples/tests/ex214.c as suggested here in the forum.  For test purposes I read a matrix with the dimension 10x10, which only has entries on the main diagonal, because I know the inverse of it.
But now I have a problem using the MatMumpsGetInverse() function. I get the error message:
Error reported by MUMPS in solve phase: INFOG(1)=-47 INFO(2)=1 ACcording to the MUMPS Docu this message tells me that I would ignored the constraint NRHS= N. I checked the shape of spRHST but they appear to be correct.  Does anyone see the error?
My code is appended below.
static char help[] ="Compute a part of the inverse of a sparse matrix. This code requires that PETSc was configured with MUMPS since we are dealing with large matrices \
and therefore use a parallel LU factorization. We compute the inverse by solving the equation A*X=RHS. Where A is our Matrix, X is the inverse and RHS is the identity matrix.\
Note that the number of columns nrhs of X can be chosen smaller than the number of columns N in A. Therefore only a part of the inverse is computed in X. \n \
In this code we use a sparse representation of the RHS matrix in MUMPS in csr format. Computation of selected entries in inv(A) is done using MatMumpsGetInverse. \n \
Input parameters: \n\
-fin <input_file> : file to load \n \
-fout <input_file> : file to load \n \
-nrhs <numberofcolumns> : Number of columns to compute \n \
-displ <Bool>: Print matrices to terminal \n\
Example usage: \n \
mpiexec -np 2 ./compute_inverse_sparse_rhs -fin ../../convert_to_binary_petsc_matrix/identity_matrix_prefactor3_ncols10 -nrhs 5 -displ";

#include <stdio.h>
#include <petscmat.h>
#include <petscviewer.h>

int main(int argc, char **args){
PetscErrorCode ierr; // Datatype used for return error code
PetscMPIInt size,rank; // Datatype used to represent 'int' parameters to MPI functions.
#if defined(PETSC_HAVE_MUMPS)
Mat A,F,spRHST; // Abstract PETSc matrix object used to manage all linear operators in PETSc
PetscViewer fd; // Abstract PETSc object that helps view (in ASCII, binary, graphically etc) other PETSc objects
PetscBool       flg1,flg2; // Logical variable. Actually an int in C.
PetscBool displ=PETSC_FALSE; // Display matrices
PetscInt M,N,m,n,rstart,rend,nrhs,i; // PETSc type that represents an integer, used primarily to represent size of arrays and indexing into arrays.
PetscScalar         v;                               // PETSc type that represents either a double precision real number,...
char inputfile[1][PETSC_MAX_PATH_LEN]; // Input file name
//  char outputfile[1][PETSC_MAX_PATH_LEN]; // Outputfile file name
#endif

// Initializes PETSc and MPI. Get size and rank of MPI.
ierr = PetscInitialize(&argc, &args, (char*)0, help);if (ierr){return ierr;}
ierr = MPI_Comm_size(PETSC_COMM_WORLD, &size);CHKERRQ(ierr);
ierr = MPI_Comm_rank(PETSC_COMM_WORLD,&rank);CHKERRQ(ierr);

//Check if PETSc was configured with MUMPS. If not print error message and exit
#if !defined(PETSC_HAVE_MUMPS)
if (!=rank){ierr = PetscPrintf(PETSC_COMM_SELF, "This code requires MUMPS, exit...\n");CHKERRQ(ierr);
ierr = PetscFinalize();
return ierr;
}
#else

// Check if displ is set. If True the matrices are printed to the terminal
ierr = PetscOptionsGetBool(NULL, NULL, "-displ", &displ, NULL);CHKERRQ(ierr);

// Load matrix A from file
ierr = PetscOptionsGetString(NULL, NULL, "-fin" ,inputfile[0], PETSC_MAX_PATH_LEN, &flg1);CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD, "Load matrix in: %s \n", inputfile[0]);CHKERRQ(ierr);
ierr = PetscViewerBinaryOpen(PETSC_COMM_WORLD, inputfile[0], FILE_MODE_READ, &fd);CHKERRQ(ierr);
ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
ierr = MatSetType(A, MATAIJ);CHKERRQ(ierr);
// Print matrix A
if (displ){
ierr = PetscPrintf(PETSC_COMM_WORLD, "\n---------------\n");CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD,"Matrix A from file:\n", nrhs);
ierr = MatView(A, PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD, "\n");CHKERRQ(ierr);
}
// Check if matrix is quadratic
ierr = MatGetSize(A, &M, &N);CHKERRQ(ierr);
ierr = MatGetLocalSize(A, &m, &n);CHKERRQ(ierr);
if (M != N){
//Macro that is called when an error has been detected.
SETERRQ2(PETSC_COMM_SELF, PETSC_ERR_ARG_SIZ, "Detected a rectangular matrix: (%d, %d)", M, N);
}
ierr = MatGetOwnershipRange(A,&rstart,&rend);CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD, "---------------\n");CHKERRQ(ierr);
ierr = PetscSynchronizedPrintf(PETSC_COMM_WORLD, "Ownership ranges for Matrix A, rank:  %i, size: %i, rstart: %i, rend: %i \n", rank, size, rstart, rend);CHKERRQ(ierr);
ierr = PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT);CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD, "---------------\n");CHKERRQ(ierr);

// Set the number of columns of the inverse to be computed.
nrhs = N;
ierr = PetscOptionsGetInt(NULL, NULL, "-nrhs", &nrhs, &flg2);CHKERRQ(ierr);

// Create SpRHST for inv(A) with sparse RHS stored in the host.
// PETSc does not support compressed column format which is required by MUMPS for sparse RHS matrix,
// thus user must create spRHST=spRHS^T and call MatMatTransposeSolve()
// User must create B^T in sparse compressed row format on the host processor and call MatMatTransposeSolve() to implement MUMPS' MatMatSolve().
// MUMPS requires nrhs = N
ierr = MatCreate(PETSC_COMM_WORLD, &spRHST);CHKERRQ(ierr);
if (!rank){
ierr = MatSetSizes(spRHST,N,M,PETSC_DECIDE,PETSC_DECIDE);CHKERRQ(ierr);
}
else{
ierr = MatSetSizes(spRHST,0,0,PETSC_DECIDE,PETSC_DECIDE);CHKERRQ(ierr);
}
ierr = MatSetType(spRHST,MATAIJ);CHKERRQ(ierr);
ierr = MatSetFromOptions(spRHST);CHKERRQ(ierr);
ierr = MatSetUp(spRHST);CHKERRQ(ierr);
if (!rank){
v = 1.0;
for(i=0;i<nrhs;i++){
ierr = MatSetValues(spRHST,1,&i,1,&i,&v,INSERT_VALUES);CHKERRQ(ierr);
}
}
ierr = MatAssemblyBegin(spRHST,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
ierr = MatAssemblyEnd(spRHST, MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);

// Print matrix spRHST
if (displ){
ierr = PetscPrintf(PETSC_COMM_WORLD, "\n---------------\n");CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD,"Matrix spRHST:\n", nrhs);
ierr = MatView(spRHST, PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD, "\n");CHKERRQ(ierr);
}

// Print information
ierr = PetscPrintf(PETSC_COMM_WORLD, "\nCompute %i columns of the inverse using LU-factorization in MUMPS!\n", nrhs);

// Factorize the Matrix using a parallel LU factorization in MUMPS
ierr = MatGetFactor(A, MATSOLVERMUMPS, MAT_FACTOR_LU, &F);CHKERRQ(ierr);
ierr = MatLUFactorSymbolic(F, A, NULL, NULL, NULL);CHKERRQ(ierr);
ierr = MatLUFactorNumeric(F, A, NULL);CHKERRQ(ierr);

// Create spRHS
Mat spRHS = NULL;

// Create spRHS = spRHS^T. Two matrices that share internal matrix data structure.
// Creates a new matrix object that behaves like A'.
ierr = MatCreateTranspose(spRHST,&spRHS);CHKERRQ(ierr);

// Get user-specified set of entries in inverse of A
ierr = MatMumpsGetInverse(F,spRHS);CHKERRQ(ierr);

if (displ){
ierr = PetscPrintf(PETSC_COMM_WORLD, "\n---------------\n");CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD,"First %D columns of inv(A) with sparse RHS:\n", nrhs);
ierr = MatView(spRHS,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
ierr = PetscPrintf(PETSC_COMM_WORLD, "---------------\n");CHKERRQ(ierr);
}

// Free data structures
ierr = MatDestroy(&A);CHKERRQ(ierr);
ierr = MatDestroy(&spRHS);CHKERRQ(ierr);
ierr = MatDestroy(&spRHST);CHKERRQ(ierr);
ierr = PetscFinalize();
return ierr;

#endif
}

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