#include <iostream>

#include "petsc.h"

int main(int argc, char** argv)
{
    PetscCall(PetscInitialize(&argc, &argv, nullptr, nullptr));

    PetscInt    m   = 2;
    PetscInt    n   = 2;
    PetscInt    i[] = {0, 2, 4};
    PetscInt    j[] = {1, 0, 0, 1};
    PetscScalar v[] = {2, 1, 3, 4};

    Mat mat;
    PetscCall(MatCreateMPIAIJWithArrays(PETSC_COMM_SELF, m, n, m, n, i, j, v, &mat));

    std::cout << "=== Before update ===" << std::endl;
    for (PetscInt row = 0; row < m; ++row)
    {
        for (PetscInt col = 0; col < n; ++col)
        {
            PetscScalar x;
            PetscCall(MatGetValue(mat, row, col, &x));
            std::cout << ' ' << x;
        }
        std::cout << std::endl;
    }

    PetscCall(MatUpdateMPIAIJWithArray(mat, v));

    std::cout << "=== After update ===" << std::endl;
    for (PetscInt row = 0; row < m; ++row)
    {
        for (PetscInt col = 0; col < n; ++col)
        {
            PetscScalar x;
            PetscCall(MatGetValue(mat, row, col, &x));
            std::cout << ' ' << x;
        }
        std::cout << std::endl;
    }

    PetscCall(MatDestroy(&mat));

    PetscCall(PetscFinalize());
}