Actual source code: ex3.c

  1: static char help[] = "Solves the 1-dimensional wave equation.\n\n";

  3: #include <petscdm.h>
  4: #include <petscdmda.h>
  5: #include <petscdraw.h>

  7: int main(int argc, char **argv)
  8: {
  9:   PetscMPIInt  rank, size;
 10:   PetscInt     M = 60, time_steps = 100, localsize, j, i, mybase, myend, *localnodes = NULL;
 11:   int          width, xbase;
 12:   DM           da;
 13:   PetscViewer  viewer, viewer_private;
 14:   PetscDraw    draw;
 15:   Vec          local, global;
 16:   PetscScalar *localptr, *globalptr;
 17:   PetscReal    a, h, k;
 18:   PetscBool    flg = PETSC_FALSE;

 20:   PetscFunctionBeginUser;
 21:   PetscCall(PetscInitialize(&argc, &argv, NULL, help));
 22:   PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));
 23:   PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));

 25:   PetscCall(PetscOptionsGetInt(NULL, NULL, "-M", &M, NULL));
 26:   PetscCall(PetscOptionsGetInt(NULL, NULL, "-time", &time_steps, NULL));
 27:   /*
 28:       Test putting two nodes on each processor, exact last processor gets the rest
 29:   */
 30:   PetscCall(PetscOptionsGetBool(NULL, NULL, "-distribute", &flg, NULL));
 31:   if (flg) {
 32:     PetscCall(PetscMalloc1(size, &localnodes));
 33:     for (i = 0; i < size - 1; i++) localnodes[i] = 2;
 34:     localnodes[size - 1] = M - 2 * (size - 1);
 35:   }

 37:   /* Set up the array */
 38:   PetscCall(DMDACreate1d(PETSC_COMM_WORLD, DM_BOUNDARY_PERIODIC, M, 1, 1, localnodes, &da));
 39:   PetscCall(DMSetFromOptions(da));
 40:   PetscCall(DMSetUp(da));
 41:   PetscCall(PetscFree(localnodes));
 42:   PetscCall(DMCreateGlobalVector(da, &global));
 43:   PetscCall(DMCreateLocalVector(da, &local));

 45:   /* Set up display to show combined wave graph */
 46:   PetscCall(PetscViewerDrawOpen(PETSC_COMM_WORLD, 0, "Entire Solution", 20, 480, 800, 200, &viewer));
 47:   PetscCall(PetscViewerDrawGetDraw(viewer, 0, &draw));
 48:   PetscCall(PetscDrawSetDoubleBuffer(draw));

 50:   /* determine starting point of each processor */
 51:   PetscCall(VecGetOwnershipRange(global, &mybase, &myend));

 53:   /* set up display to show my portion of the wave */
 54:   xbase = (int)((mybase) * ((800.0 - 4.0 * size) / M) + 4.0 * rank);
 55:   width = (int)((myend - mybase) * 800. / M);
 56:   PetscCall(PetscViewerDrawOpen(PETSC_COMM_SELF, 0, "Local Portion of Solution", xbase, 200, width, 200, &viewer_private));
 57:   PetscCall(PetscViewerDrawGetDraw(viewer_private, 0, &draw));
 58:   PetscCall(PetscDrawSetDoubleBuffer(draw));

 60:   /* Initialize the array */
 61:   PetscCall(VecGetLocalSize(local, &localsize));
 62:   PetscCall(VecGetArray(global, &globalptr));

 64:   for (i = 1; i < localsize - 1; i++) {
 65:     j                = (i - 1) + mybase;
 66:     globalptr[i - 1] = PetscSinReal((PETSC_PI * j * 6) / ((PetscReal)M) + 1.2 * PetscSinReal((PETSC_PI * j * 2) / ((PetscReal)M))) * 2;
 67:   }

 69:   PetscCall(VecRestoreArray(global, &globalptr));

 71:   /* Assign Parameters */
 72:   a = 1.0;
 73:   h = 1.0 / M;
 74:   k = h;

 76:   for (j = 0; j < time_steps; j++) {
 77:     /* Global to Local */
 78:     PetscCall(DMGlobalToLocalBegin(da, global, INSERT_VALUES, local));
 79:     PetscCall(DMGlobalToLocalEnd(da, global, INSERT_VALUES, local));

 81:     /*Extract local array */
 82:     PetscCall(VecGetArray(local, &localptr));
 83:     PetscCall(VecGetArray(global, &globalptr));

 85:     /* Update Locally - Make array of new values */
 86:     /* Note: I don't do anything for the first and last entry */
 87:     for (i = 1; i < localsize - 1; i++) globalptr[i - 1] = .5 * (localptr[i + 1] + localptr[i - 1]) - (k / (2.0 * a * h)) * (localptr[i + 1] - localptr[i - 1]);
 88:     PetscCall(VecRestoreArray(global, &globalptr));
 89:     PetscCall(VecRestoreArray(local, &localptr));

 91:     /* View my part of Wave */
 92:     PetscCall(VecView(global, viewer_private));

 94:     /* View global Wave */
 95:     PetscCall(VecView(global, viewer));
 96:   }

 98:   PetscCall(DMDestroy(&da));
 99:   PetscCall(PetscViewerDestroy(&viewer));
100:   PetscCall(PetscViewerDestroy(&viewer_private));
101:   PetscCall(VecDestroy(&local));
102:   PetscCall(VecDestroy(&global));

104:   PetscCall(PetscFinalize());
105:   return 0;
106: }

108: /*TEST

110:     test:
111:       nsize: 3
112:       args: -time 50 -nox
113:       requires: x

115: TEST*/