Hello everyone, Does anyone here know how one can write a complex or real, matrix or vector (matrix could be sparse or full) in MATLAB to a binary file such that it can be read correctly by PETSc? I tried using PetscBinaryWrite.m that came with PETSc ( /bin/matlab) to write a simple real (or complex), full (or sparse) matrix in binary file named 'matrix.dat' and tried reading it in PETSc, but it absolutely does not work :( I did PetscBinaryWrite('matrix.dat', C) to write a matrix C in an empty file named 'matrix.dat' in MATLAB. Then I tried reading 'matrix.dat' file in PETSc using the following command : PetscViewer binviewer ; Mat C ; char fileC[PETSC_MAX_PATH_LEN] ; ierr = PetscOptionsGetString(PETSC_NULL, "-fC", fileC, PETSC_MAX_PATH_LEN-1, PETSC_NULL) ; CHKERRQ(ierr) ; ierr = PetscViewerBinaryOpen(PETSC_COMM_WORLD, fileC, FILE_MODE_READ, &binviewer) ; CHKERRQ(ierr) ; ierr = MatLoad(binviewer, MATMPIAIJ, &C) ; CHKERRQ(ierr) ; I must add that I compiled PETSc with complex numbers. I plan on assembling my matrix (very large square sparse matrix, size greater than 1e+8) in MATLAB, which does not take too long to assemble in MATLAB at all. Then I will write the matrix to a binary file and read that in PETSc and solve a very large linear system of equations in parallel in PETSc using MPI. Hence, I really need to be able to write the matrix in MATLAB to a binary file such that PETSc can correctly read the matrix. I am really surprised to find out that PETSc cannot read/write a matrix or vector, full or sparse, real or complex in MATRIX MARKET FORMAT. I have gone though the manual, googled around quite a bit, but I just have not found anything useful. I will truly appreciate any help or a pointer in this regard. Thank you. Amrit