main.c

static char help[] = "Basic vector routines.\n\n";

/*
  Include "petscvec.h" so that we can use vectors.  Note that this file
  automatically includes:
     petscsys.h       - base PETSc routines   petscis.h     - index sets
     petscviewer.h - viewers
*/

#include <lapacke.h>
#include <stdio.h>
#include <stdlib.h>

#include <petscvec.h>

int example_lapack() {
    int n = 2;    // Dimension of the matrix A
    int nrhs = 1; // Number of right-hand sides
    int lda = 2;  // Leading dimension of A
    int ldb = 2;  // Leading dimension of B
    int info;     // Status output
    int ipiv[2];  // Pivot indices for the LU decomposition

    // Define matrix A (row-major order)
    double A[4] = {3, 1, 1, 2};

    // Define right-hand side vector b
    double b[2] = {9, 8};

    // Call LAPACK dgesv to solve Ax = b
    info = LAPACKE_dgesv(LAPACK_ROW_MAJOR, n, nrhs, A, lda, ipiv, b, ldb);

    // Check for success
    if (info == 0) {
        printf("Solution:\n");
        for (int i = 0; i < n; i++) {
            printf("x[%d] = %f\n", i, b[i]);
        }
    } else if (info < 0) {
        printf("Argument %d had an illegal value.\n", -info);
    } else {
        printf("Matrix is singular. Solution could not be computed.\n");
    }

    return info;
}

int main(int argc, char **argv) {
    printf("LAPACKE Example:\n");
    example_lapack();

    printf("PETSC Example:\n");
    Vec x, y, w; /* vectors */
    Vec *z;      /* array of vectors */
    PetscReal norm, v, v1, v2, maxval;
    PetscInt n = 20, maxind;
    PetscScalar one = 1.0, two = 2.0, three = 3.0, dots[3], dot;

    PetscFunctionBeginUser;
    PetscCall(PetscInitialize(&argc, &argv, NULL, help));
    PetscCall(PetscOptionsGetInt(NULL, NULL, "-n", &n, NULL));

    /*
       Create a vector, specifying only its global dimension.
       When using VecCreate(), VecSetSizes() and VecSetFromOptions(), the vector
       format (currently parallel, shared, or sequential) is determined at
       runtime.  Also, the parallel partitioning of the vector is determined by
       PETSc at runtime.
    */
    PetscCall(VecCreate(PETSC_COMM_WORLD, &x));
    PetscCall(VecSetSizes(x, PETSC_DECIDE, n));
    PetscCall(VecSetFromOptions(x));

    /*
       Duplicate some work vectors (of the same format and
       partitioning as the initial vector).
    */
    PetscCall(VecDuplicate(x, &y));
    PetscCall(VecDuplicate(x, &w));

    /*
       Duplicate more work vectors (of the same format and
       partitioning as the initial vector).  Here we duplicate
       an array of vectors, which is often more convenient than
       duplicating individual ones.
    */
    PetscCall(VecDuplicateVecs(x, 3, &z));
    /*
       Set the vectors to entries to a constant value.
    */
    PetscCall(VecSet(x, one));
    PetscCall(VecSet(y, two));
    PetscCall(VecSet(z[0], one));
    PetscCall(VecSet(z[1], two));
    PetscCall(VecSet(z[2], three));
    /*
       Demonstrate various basic vector routines.
    */
    PetscCall(VecDot(x, y, &dot));
    PetscCall(VecMDot(x, 3, z, dots));

    /*
       Note: If using a complex numbers version of PETSc, then
       PETSC_USE_COMPLEX is defined in the makefiles; otherwise,
       (when using real numbers) it is undefined.
    */

    PetscCall(
        PetscPrintf(PETSC_COMM_WORLD, "Vector length %" PetscInt_FMT "\n", n));
    PetscCall(VecMax(x, &maxind, &maxval));
    PetscCall(PetscPrintf(PETSC_COMM_WORLD,
                          "VecMax %g, VecInd %" PetscInt_FMT "\n",
                          (double)maxval, maxind));

    PetscCall(VecMin(x, &maxind, &maxval));
    PetscCall(PetscPrintf(PETSC_COMM_WORLD,
                          "VecMin %g, VecInd %" PetscInt_FMT "\n",
                          (double)maxval, maxind));
    PetscCall(PetscPrintf(PETSC_COMM_WORLD,
                          "All other values should be near zero\n"));

    PetscCall(VecScale(x, two));
    PetscCall(VecNorm(x, NORM_2, &norm));
    v = norm - 2.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "VecScale %g\n", (double)v));

    PetscCall(VecCopy(x, w));
    PetscCall(VecNorm(w, NORM_2, &norm));
    v = norm - 2.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "VecCopy  %g\n", (double)v));

    PetscCall(VecAXPY(y, three, x));
    PetscCall(VecNorm(y, NORM_2, &norm));
    v = norm - 8.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "VecAXPY %g\n", (double)v));

    PetscCall(VecAYPX(y, two, x));
    PetscCall(VecNorm(y, NORM_2, &norm));
    v = norm - 18.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "VecAYPX %g\n", (double)v));

    PetscCall(VecSwap(x, y));
    PetscCall(VecNorm(y, NORM_2, &norm));
    v = norm - 2.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "VecSwap  %g\n", (double)v));
    PetscCall(VecNorm(x, NORM_2, &norm));
    v = norm - 18.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "VecSwap  %g\n", (double)v));

    PetscCall(VecWAXPY(w, two, x, y));
    PetscCall(VecNorm(w, NORM_2, &norm));
    v = norm - 38.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "VecWAXPY %g\n", (double)v));

    PetscCall(VecPointwiseMult(w, y, x));
    PetscCall(VecNorm(w, NORM_2, &norm));
    v = norm - 36.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(
        PetscPrintf(PETSC_COMM_WORLD, "VecPointwiseMult %g\n", (double)v));

    PetscCall(VecPointwiseDivide(w, x, y));
    PetscCall(VecNorm(w, NORM_2, &norm));
    v = norm - 9.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(
        PetscPrintf(PETSC_COMM_WORLD, "VecPointwiseDivide %g\n", (double)v));

    PetscCall(VecSetValue(y, 0, 0.0, INSERT_VALUES));
    PetscCall(VecAssemblyBegin(y));
    PetscCall(VecAssemblyEnd(y));
    PetscCall(VecPointwiseDivide(w, x, y));
    PetscCall(VecNorm(w, NORM_2, &norm));
    v = norm - 9.0 * PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(
        PetscPrintf(PETSC_COMM_WORLD, "VecPointwiseDivide %g\n", (double)v));

    dots[0] = one;
    dots[1] = three;
    dots[2] = two;

    PetscCall(VecSet(x, one));
    PetscCall(VecMAXPY(x, 3, dots, z));
    PetscCall(VecNorm(z[0], NORM_2, &norm));
    v = norm - PetscSqrtReal((PetscReal)n);
    if (v > -PETSC_SMALL && v < PETSC_SMALL)
        v = 0.0;
    PetscCall(VecNorm(z[1], NORM_2, &norm));
    v1 = norm - 2.0 * PetscSqrtReal((PetscReal)n);
    if (v1 > -PETSC_SMALL && v1 < PETSC_SMALL)
        v1 = 0.0;
    PetscCall(VecNorm(z[2], NORM_2, &norm));
    v2 = norm - 3.0 * PetscSqrtReal((PetscReal)n);
    if (v2 > -PETSC_SMALL && v2 < PETSC_SMALL)
        v2 = 0.0;
    PetscCall(PetscPrintf(PETSC_COMM_WORLD, "VecMAXPY %g %g %g \n", (double)v,
                          (double)v1, (double)v2));

    /*
       Free work space.  All PETSc objects should be destroyed when they
       are no longer needed.
    */
    PetscCall(VecDestroy(&x));
    PetscCall(VecDestroy(&y));
    PetscCall(VecDestroy(&w));
    PetscCall(VecDestroyVecs(3, &z));
    PetscCall(PetscFinalize());
    return 0;
}

/*TEST

  testset:
    output_file: output/ex1_1.out
    # This is a test where the exact numbers are critical
    diff_args: -j

    test:

    test:
        suffix: cuda
        args: -vec_type cuda
        requires: cuda

    test:
        suffix: kokkos
        args: -vec_type kokkos
        requires: kokkos_kernels

    test:
        suffix: hip
        args: -vec_type hip
        requires: hip

    test:
        suffix: 2
        nsize: 2

    test:
        suffix: 2_cuda
        nsize: 2
        args: -vec_type cuda
        requires: cuda

    test:
        suffix: 2_kokkos
        nsize: 2
        args: -vec_type kokkos
        requires: kokkos_kernels

    test:
        suffix: 2_hip
        nsize: 2
        args: -vec_type hip
        requires: hip

TEST*/