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101 lines
3.0 KiB
C
101 lines
3.0 KiB
C
static char help[] = "Solves a tridiagonal linear system with KSP.\n\n";
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#include <petscksp.h>
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#include <petscerror.h>
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int main(int argc, char **args)
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{
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Vec x, b, u; /* approx solution, RHS, exact solution */
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Mat A; /* linear system matrix */
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KSP ksp; /* linear solver context */
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PC pc; /* preconditioner context */
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PetscReal norm; /* norm of solution error */
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PetscInt i, n = 10, col[3], its;
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PetscMPIInt size;
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PetscScalar value[3];
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PetscFunctionBeginUser;
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PetscCall(PetscInitialize(&argc, &args, (char *)0, help));
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PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
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PetscCheck(size == 1, PETSC_COMM_WORLD, PETSC_ERR_WRONG_MPI_SIZE, "This is a uniprocessor example only!");
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PetscCall(PetscOptionsGetInt(NULL, NULL, "-n", &n, NULL));
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PetscCall(VecCreate(PETSC_COMM_SELF, &x));
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PetscCall(PetscObjectSetName((PetscObject)x, "Solution"));
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PetscCall(VecSetSizes(x, PETSC_DECIDE, n));
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PetscCall(VecSetFromOptions(x));
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PetscCall(VecDuplicate(x, &b));
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PetscCall(VecDuplicate(x, &u));
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PetscCall(MatCreate(PETSC_COMM_SELF, &A));
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PetscCall(MatSetSizes(A, PETSC_DECIDE, PETSC_DECIDE, n, n));
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PetscCall(MatSetFromOptions(A));
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PetscCall(MatSetUp(A));
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value[0] = -1.0;
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value[1] = 2.0;
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value[2] = -1.0;
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for (i = 1; i < n - 1; i++) {
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col[0] = i - 1;
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col[1] = i;
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col[2] = i + 1;
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PetscCall(MatSetValues(A, 1, &i, 3, col, value, INSERT_VALUES));
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}
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i = n - 1;
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col[0] = n - 2;
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col[1] = n - 1;
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PetscCall(MatSetValues(A, 1, &i, 2, col, value, INSERT_VALUES));
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i = 0;
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col[0] = 0;
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col[1] = 1;
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value[0] = 2.0;
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value[1] = -1.0;
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PetscCall(MatSetValues(A, 1, &i, 2, col, value, INSERT_VALUES));
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PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
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PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
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PetscCall(VecSet(u, 1.0));
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PetscCall(MatMult(A, u, b));
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PetscCall(KSPCreate(PETSC_COMM_SELF, &ksp));
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PetscCall(KSPSetOperators(ksp, A, A));
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PetscCall(KSPGetPC(ksp, &pc));
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PetscCall(PCSetType(pc, PCJACOBI));
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PetscCall(KSPSetTolerances(ksp, 1.e-5, PETSC_DEFAULT, PETSC_DEFAULT, PETSC_DEFAULT));
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PetscCall(KSPSetFromOptions(ksp));
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PetscCall(KSPSolve(ksp, b, x));
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PetscCall(VecAXPY(x, -1.0, u));
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PetscCall(VecNorm(x, NORM_2, &norm));
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PetscCall(KSPGetIterationNumber(ksp, &its));
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PetscCall(PetscPrintf(PETSC_COMM_SELF, "Norm of error %g, Iterations %" PetscInt_FMT "\n", (double)norm, its));
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PetscCall(MatShift(A, 2.0));
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PetscCall(KSPSolve(ksp, b, x));
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PetscCall(KSPDestroy(&ksp));
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if (PCMPIServerActive) {
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PetscCall(KSPCreate(PETSC_COMM_SELF, &ksp));
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PetscCall(KSPSetOptionsPrefix(ksp, "prefix_test_"));
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PetscCall(MatSetOptionsPrefix(A, "prefix_test_"));
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PetscCall(KSPSetOperators(ksp, A, A));
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PetscCall(KSPSetFromOptions(ksp));
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PetscCall(KSPSolve(ksp, b, x));
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PetscCall(KSPDestroy(&ksp));
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}
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PetscCall(VecDestroy(&x));
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PetscCall(VecDestroy(&u));
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PetscCall(VecDestroy(&b));
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PetscCall(MatDestroy(&A));
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PetscCall(PetscFinalize());
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return 0;
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}
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