1 2 static char help[] = "\n\n"; 3 4 /* 5 Demonstrates using DM_BOUNDARY_GHOSTED how to handle a rotated boundary conditions where one edge 6 is connected to its immediate neighbor 7 8 Consider the domain (with natural numbering) 9 10 6 7 8 11 3 4 5 12 0 1 2 13 14 The ghost points along the bottom (directly below the three columns above) should be 0 3 and 6 15 while the ghost points along the left side should be 0 1 2 16 17 Note that the ghosted local vectors extend in both the x and y directions so, for example if we have a 18 single MPI process the ghosted vector has (in the original natural numbering) 19 20 x x x x x 21 2 6 7 8 x 22 1 3 4 5 x 23 0 0 1 2 x 24 x 0 3 6 x 25 26 where x indicates a location that is not updated by the communication and should be used. 27 28 For this to make sense the number of grid points in the x and y directions must be the same 29 30 This ghost point mapping was suggested by: Wenbo Zhao <zhaowenbo.npic@gmail.com> 31 */ 32 33 #include <petscdm.h> 34 #include <petscdmda.h> 35 36 int main(int argc, char **argv) { 37 PetscInt M = 6; 38 DM da; 39 Vec local, global, natural; 40 PetscInt i, start, end, *ifrom, x, y, xm, ym; 41 PetscScalar *xnatural; 42 IS from, to; 43 AO ao; 44 VecScatter scatter1, scatter2; 45 PetscViewer subviewer; 46 47 PetscFunctionBeginUser; 48 PetscCall(PetscInitialize(&argc, &argv, (char *)0, help)); 49 50 /* Create distributed array and get vectors */ 51 PetscCall(DMDACreate2d(PETSC_COMM_WORLD, DM_BOUNDARY_GHOSTED, DM_BOUNDARY_GHOSTED, DMDA_STENCIL_STAR, M, M, PETSC_DECIDE, PETSC_DECIDE, 1, 1, NULL, NULL, &da)); 52 PetscCall(DMSetUp(da)); 53 PetscCall(DMCreateGlobalVector(da, &global)); 54 PetscCall(DMCreateLocalVector(da, &local)); 55 56 /* construct global to local scatter for the left side of the domain to the ghost on the bottom */ 57 PetscCall(DMDAGetCorners(da, &x, &y, NULL, &xm, &ym, NULL)); 58 if (!y) { /* only processes on the bottom of the domain fill up the ghost locations */ 59 PetscCall(ISCreateStride(PETSC_COMM_SELF, xm, 1, 1, &to)); 60 } else { 61 PetscCall(ISCreateStride(PETSC_COMM_SELF, 0, 0, 0, &to)); 62 } 63 PetscCall(PetscMalloc1(xm, &ifrom)); 64 for (i = x; i < x + xm; i++) ifrom[i - x] = M * i; 65 PetscCall(DMDAGetAO(da, &ao)); 66 PetscCall(AOApplicationToPetsc(ao, xm, ifrom)); 67 if (!y) { 68 PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, xm, ifrom, PETSC_OWN_POINTER, &from)); 69 } else { 70 PetscCall(PetscFree(ifrom)); 71 PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, 0, NULL, PETSC_COPY_VALUES, &from)); 72 } 73 PetscCall(VecScatterCreate(global, from, local, to, &scatter1)); 74 PetscCall(ISDestroy(&to)); 75 PetscCall(ISDestroy(&from)); 76 77 /* construct global to local scatter for the bottom side of the domain to the ghost on the right */ 78 if (!x) { /* only processes on the left side of the domain fill up the ghost locations */ 79 PetscCall(ISCreateStride(PETSC_COMM_SELF, ym, xm + 2, xm + 2, &to)); 80 } else { 81 PetscCall(ISCreateStride(PETSC_COMM_SELF, 0, 0, 0, &to)); 82 } 83 PetscCall(PetscMalloc1(ym, &ifrom)); 84 for (i = y; i < y + ym; i++) ifrom[i - y] = i; 85 PetscCall(DMDAGetAO(da, &ao)); 86 PetscCall(AOApplicationToPetsc(ao, ym, ifrom)); 87 if (!x) { 88 PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, ym, ifrom, PETSC_OWN_POINTER, &from)); 89 } else { 90 PetscCall(PetscFree(ifrom)); 91 PetscCall(ISCreateGeneral(PETSC_COMM_WORLD, 0, NULL, PETSC_COPY_VALUES, &from)); 92 } 93 PetscCall(VecScatterCreate(global, from, local, to, &scatter2)); 94 PetscCall(ISDestroy(&to)); 95 PetscCall(ISDestroy(&from)); 96 97 /* 98 fill the global vector with the natural global numbering for each local entry 99 this is only done for testing purposes since it is easy to see if the scatter worked correctly 100 */ 101 PetscCall(DMDACreateNaturalVector(da, &natural)); 102 PetscCall(VecGetOwnershipRange(natural, &start, &end)); 103 PetscCall(VecGetArray(natural, &xnatural)); 104 for (i = start; i < end; i++) xnatural[i - start] = i; 105 PetscCall(VecRestoreArray(natural, &xnatural)); 106 PetscCall(DMDANaturalToGlobalBegin(da, natural, INSERT_VALUES, global)); 107 PetscCall(DMDANaturalToGlobalEnd(da, natural, INSERT_VALUES, global)); 108 PetscCall(VecDestroy(&natural)); 109 110 /* scatter from global to local */ 111 PetscCall(VecScatterBegin(scatter1, global, local, INSERT_VALUES, SCATTER_FORWARD)); 112 PetscCall(VecScatterEnd(scatter1, global, local, INSERT_VALUES, SCATTER_FORWARD)); 113 PetscCall(VecScatterBegin(scatter2, global, local, INSERT_VALUES, SCATTER_FORWARD)); 114 PetscCall(VecScatterEnd(scatter2, global, local, INSERT_VALUES, SCATTER_FORWARD)); 115 /* 116 normally here you would also call 117 PetscCall(DMGlobalToLocalBegin(da,global,INSERT_VALUES,local)); 118 PetscCall(DMGlobalToLocalEnd(da,global,INSERT_VALUES,local)); 119 to update all the interior ghost cells between neighboring processes. 120 We don't do it here since this is only a test of "special" ghost points. 121 */ 122 123 /* view each local ghosted vector */ 124 PetscCall(PetscViewerGetSubViewer(PETSC_VIEWER_STDOUT_WORLD, PETSC_COMM_SELF, &subviewer)); 125 PetscCall(VecView(local, subviewer)); 126 PetscCall(PetscViewerRestoreSubViewer(PETSC_VIEWER_STDOUT_WORLD, PETSC_COMM_SELF, &subviewer)); 127 128 PetscCall(VecScatterDestroy(&scatter1)); 129 PetscCall(VecScatterDestroy(&scatter2)); 130 PetscCall(VecDestroy(&local)); 131 PetscCall(VecDestroy(&global)); 132 PetscCall(DMDestroy(&da)); 133 PetscCall(PetscFinalize()); 134 return 0; 135 } 136 137 /*TEST 138 139 test: 140 141 test: 142 suffix: 2 143 nsize: 2 144 145 test: 146 suffix: 4 147 nsize: 4 148 149 test: 150 suffix: 9 151 nsize: 9 152 153 TEST*/ 154