1 2 static char help[] = "Demonstrates use of VecCreateGhost().\n\n"; 3 4 /* 5 Description: Ghost padding is one way to handle local calculations that 6 involve values from other processors. VecCreateGhost() provides 7 a way to create vectors with extra room at the end of the vector 8 array to contain the needed ghost values from other processors, 9 vector computations are otherwise unaffected. 10 */ 11 12 /* 13 Include "petscvec.h" so that we can use vectors. Note that this file 14 automatically includes: 15 petscsys.h - base PETSc routines petscis.h - index sets 16 petscviewer.h - viewers 17 */ 18 #include <petscvec.h> 19 20 int main(int argc,char **argv) 21 { 22 PetscMPIInt rank,size; 23 PetscInt nlocal = 6,nghost = 2,ifrom[2],i,rstart,rend; 24 PetscBool flg,flg2,flg3; 25 PetscScalar value,*array,*tarray=0; 26 Vec lx,gx,gxs; 27 28 PetscFunctionBeginUser; 29 PetscCall(PetscInitialize(&argc,&argv,(char*)0,help)); 30 PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD,&rank)); 31 PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD,&size)); 32 PetscCheck(size == 2,PETSC_COMM_WORLD,PETSC_ERR_WRONG_MPI_SIZE,"Must run example with two processors"); 33 34 /* 35 Construct a two dimensional graph connecting nlocal degrees of 36 freedom per processor. From this we will generate the global 37 indices of needed ghost values 38 39 For simplicity we generate the entire graph on each processor: 40 in real application the graph would stored in parallel, but this 41 example is only to demonstrate the management of ghost padding 42 with VecCreateGhost(). 43 44 In this example we consider the vector as representing 45 degrees of freedom in a one dimensional grid with periodic 46 boundary conditions. 47 48 ----Processor 1--------- ----Processor 2 -------- 49 0 1 2 3 4 5 6 7 8 9 10 11 50 |----| 51 |-------------------------------------------------| 52 53 */ 54 55 if (rank == 0) { 56 ifrom[0] = 11; ifrom[1] = 6; 57 } else { 58 ifrom[0] = 0; ifrom[1] = 5; 59 } 60 61 /* 62 Create the vector with two slots for ghost points. Note that both 63 the local vector (lx) and the global vector (gx) share the same 64 array for storing vector values. 65 */ 66 PetscCall(PetscOptionsHasName(NULL,NULL,"-allocate",&flg)); 67 PetscCall(PetscOptionsHasName(NULL,NULL,"-vecmpisetghost",&flg2)); 68 PetscCall(PetscOptionsHasName(NULL,NULL,"-minvalues",&flg3)); 69 if (flg) { 70 PetscCall(PetscMalloc1(nlocal+nghost,&tarray)); 71 PetscCall(VecCreateGhostWithArray(PETSC_COMM_WORLD,nlocal,PETSC_DECIDE,nghost,ifrom,tarray,&gxs)); 72 } else if (flg2) { 73 PetscCall(VecCreate(PETSC_COMM_WORLD,&gxs)); 74 PetscCall(VecSetType(gxs,VECMPI)); 75 PetscCall(VecSetSizes(gxs,nlocal,PETSC_DECIDE)); 76 PetscCall(VecMPISetGhost(gxs,nghost,ifrom)); 77 } else { 78 PetscCall(VecCreateGhost(PETSC_COMM_WORLD,nlocal,PETSC_DECIDE,nghost,ifrom,&gxs)); 79 } 80 81 /* 82 Test VecDuplicate() 83 */ 84 PetscCall(VecDuplicate(gxs,&gx)); 85 PetscCall(VecDestroy(&gxs)); 86 87 /* 88 Access the local representation 89 */ 90 PetscCall(VecGhostGetLocalForm(gx,&lx)); 91 92 /* 93 Set the values from 0 to 12 into the "global" vector 94 */ 95 PetscCall(VecGetOwnershipRange(gx,&rstart,&rend)); 96 for (i=rstart; i<rend; i++) { 97 value = (PetscScalar) i; 98 PetscCall(VecSetValues(gx,1,&i,&value,INSERT_VALUES)); 99 } 100 PetscCall(VecAssemblyBegin(gx)); 101 PetscCall(VecAssemblyEnd(gx)); 102 103 PetscCall(VecGhostUpdateBegin(gx,INSERT_VALUES,SCATTER_FORWARD)); 104 PetscCall(VecGhostUpdateEnd(gx,INSERT_VALUES,SCATTER_FORWARD)); 105 106 /* 107 Print out each vector, including the ghost padding region. 108 */ 109 PetscCall(VecGetArray(lx,&array)); 110 for (i=0; i<nlocal+nghost; i++) { 111 PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD,"%" PetscInt_FMT " %g\n",i,(double)PetscRealPart(array[i]))); 112 } 113 PetscCall(VecRestoreArray(lx,&array)); 114 PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT)); 115 PetscCall(VecGhostRestoreLocalForm(gx,&lx)); 116 117 /* Another test that sets ghost values and then accumulates onto the owning processors using MIN_VALUES */ 118 if (flg3) { 119 if (rank == 0)PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD,"\nTesting VecGhostUpdate with MIN_VALUES\n")); 120 PetscCall(VecGhostGetLocalForm(gx,&lx)); 121 PetscCall(VecGetArray(lx,&array)); 122 for (i=0; i<nghost; i++) array[nlocal+i] = rank ? (PetscScalar)4 : (PetscScalar)8; 123 PetscCall(VecRestoreArray(lx,&array)); 124 PetscCall(VecGhostRestoreLocalForm(gx,&lx)); 125 126 PetscCall(VecGhostUpdateBegin(gx,MIN_VALUES,SCATTER_REVERSE)); 127 PetscCall(VecGhostUpdateEnd(gx,MIN_VALUES,SCATTER_REVERSE)); 128 129 PetscCall(VecGhostGetLocalForm(gx,&lx)); 130 PetscCall(VecGetArray(lx,&array)); 131 132 for (i=0; i<nlocal+nghost; i++) { 133 PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD,"%" PetscInt_FMT " %g\n",i,(double)PetscRealPart(array[i]))); 134 } 135 PetscCall(VecRestoreArray(lx,&array)); 136 PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT)); 137 PetscCall(VecGhostRestoreLocalForm(gx,&lx)); 138 } 139 140 PetscCall(VecDestroy(&gx)); 141 142 if (flg) PetscCall(PetscFree(tarray)); 143 PetscCall(PetscFinalize()); 144 return 0; 145 } 146 147 /*TEST 148 149 test: 150 nsize: 2 151 152 test: 153 suffix: 2 154 nsize: 2 155 args: -allocate 156 output_file: output/ex9_1.out 157 158 test: 159 suffix: 3 160 nsize: 2 161 args: -vecmpisetghost 162 output_file: output/ex9_1.out 163 164 test: 165 suffix: 4 166 nsize: 2 167 args: -minvalues 168 output_file: output/ex9_2.out 169 requires: !complex 170 171 TEST*/ 172