1 2 static char help[] = "Demonstrates use of VecCreateGhost().\n\n"; 3 4 /*T 5 Concepts: vectors^assembling vectors; 6 Concepts: vectors^ghost padding; 7 Processors: n 8 9 Description: Ghost padding is one way to handle local calculations that 10 involve values from other processors. VecCreateGhost() provides 11 a way to create vectors with extra room at the end of the vector 12 array to contain the needed ghost values from other processors, 13 vector computations are otherwise unaffected. 14 T*/ 15 16 /* 17 Include "petscvec.h" so that we can use vectors. Note that this file 18 automatically includes: 19 petscsys.h - base PETSc routines petscis.h - index sets 20 petscviewer.h - viewers 21 */ 22 #include <petscvec.h> 23 24 int main(int argc,char **argv) 25 { 26 PetscMPIInt rank,size; 27 PetscInt nlocal = 6,nghost = 2,ifrom[2],i,rstart,rend; 28 PetscErrorCode ierr; 29 PetscBool flg,flg2,flg3; 30 PetscScalar value,*array,*tarray=0; 31 Vec lx,gx,gxs; 32 33 ierr = PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr; 34 ierr = MPI_Comm_rank(PETSC_COMM_WORLD,&rank);CHKERRMPI(ierr); 35 ierr = MPI_Comm_size(PETSC_COMM_WORLD,&size);CHKERRMPI(ierr); 36 if (size != 2) SETERRQ(PETSC_COMM_WORLD,PETSC_ERR_WRONG_MPI_SIZE,"Must run example with two processors\n"); 37 38 /* 39 Construct a two dimensional graph connecting nlocal degrees of 40 freedom per processor. From this we will generate the global 41 indices of needed ghost values 42 43 For simplicity we generate the entire graph on each processor: 44 in real application the graph would stored in parallel, but this 45 example is only to demonstrate the management of ghost padding 46 with VecCreateGhost(). 47 48 In this example we consider the vector as representing 49 degrees of freedom in a one dimensional grid with periodic 50 boundary conditions. 51 52 ----Processor 1--------- ----Processor 2 -------- 53 0 1 2 3 4 5 6 7 8 9 10 11 54 |----| 55 |-------------------------------------------------| 56 57 */ 58 59 if (rank == 0) { 60 ifrom[0] = 11; ifrom[1] = 6; 61 } else { 62 ifrom[0] = 0; ifrom[1] = 5; 63 } 64 65 /* 66 Create the vector with two slots for ghost points. Note that both 67 the local vector (lx) and the global vector (gx) share the same 68 array for storing vector values. 69 */ 70 ierr = PetscOptionsHasName(NULL,NULL,"-allocate",&flg);CHKERRQ(ierr); 71 ierr = PetscOptionsHasName(NULL,NULL,"-vecmpisetghost",&flg2);CHKERRQ(ierr); 72 ierr = PetscOptionsHasName(NULL,NULL,"-minvalues",&flg3);CHKERRQ(ierr); 73 if (flg) { 74 ierr = PetscMalloc1(nlocal+nghost,&tarray);CHKERRQ(ierr); 75 ierr = VecCreateGhostWithArray(PETSC_COMM_WORLD,nlocal,PETSC_DECIDE,nghost,ifrom,tarray,&gxs);CHKERRQ(ierr); 76 } else if (flg2) { 77 ierr = VecCreate(PETSC_COMM_WORLD,&gxs);CHKERRQ(ierr); 78 ierr = VecSetType(gxs,VECMPI);CHKERRQ(ierr); 79 ierr = VecSetSizes(gxs,nlocal,PETSC_DECIDE);CHKERRQ(ierr); 80 ierr = VecMPISetGhost(gxs,nghost,ifrom);CHKERRQ(ierr); 81 } else { 82 ierr = VecCreateGhost(PETSC_COMM_WORLD,nlocal,PETSC_DECIDE,nghost,ifrom,&gxs);CHKERRQ(ierr); 83 } 84 85 /* 86 Test VecDuplicate() 87 */ 88 ierr = VecDuplicate(gxs,&gx);CHKERRQ(ierr); 89 ierr = VecDestroy(&gxs);CHKERRQ(ierr); 90 91 /* 92 Access the local representation 93 */ 94 ierr = VecGhostGetLocalForm(gx,&lx);CHKERRQ(ierr); 95 96 /* 97 Set the values from 0 to 12 into the "global" vector 98 */ 99 ierr = VecGetOwnershipRange(gx,&rstart,&rend);CHKERRQ(ierr); 100 for (i=rstart; i<rend; i++) { 101 value = (PetscScalar) i; 102 ierr = VecSetValues(gx,1,&i,&value,INSERT_VALUES);CHKERRQ(ierr); 103 } 104 ierr = VecAssemblyBegin(gx);CHKERRQ(ierr); 105 ierr = VecAssemblyEnd(gx);CHKERRQ(ierr); 106 107 ierr = VecGhostUpdateBegin(gx,INSERT_VALUES,SCATTER_FORWARD);CHKERRQ(ierr); 108 ierr = VecGhostUpdateEnd(gx,INSERT_VALUES,SCATTER_FORWARD);CHKERRQ(ierr); 109 110 /* 111 Print out each vector, including the ghost padding region. 112 */ 113 ierr = VecGetArray(lx,&array);CHKERRQ(ierr); 114 for (i=0; i<nlocal+nghost; i++) { 115 ierr = PetscSynchronizedPrintf(PETSC_COMM_WORLD,"%D %g\n",i,(double)PetscRealPart(array[i]));CHKERRQ(ierr); 116 } 117 ierr = VecRestoreArray(lx,&array);CHKERRQ(ierr); 118 ierr = PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT);CHKERRQ(ierr); 119 ierr = VecGhostRestoreLocalForm(gx,&lx);CHKERRQ(ierr); 120 121 /* Another test that sets ghost values and then accumulates onto the owning processors using MIN_VALUES */ 122 if (flg3) { 123 if (rank == 0){ierr = PetscSynchronizedPrintf(PETSC_COMM_WORLD,"\nTesting VecGhostUpdate with MIN_VALUES\n");CHKERRQ(ierr);} 124 ierr = VecGhostGetLocalForm(gx,&lx);CHKERRQ(ierr); 125 ierr = VecGetArray(lx,&array);CHKERRQ(ierr); 126 for (i=0; i<nghost; i++) array[nlocal+i] = rank ? (PetscScalar)4 : (PetscScalar)8; 127 ierr = VecRestoreArray(lx,&array);CHKERRQ(ierr); 128 ierr = VecGhostRestoreLocalForm(gx,&lx);CHKERRQ(ierr); 129 130 ierr = VecGhostUpdateBegin(gx,MIN_VALUES,SCATTER_REVERSE);CHKERRQ(ierr); 131 ierr = VecGhostUpdateEnd(gx,MIN_VALUES,SCATTER_REVERSE);CHKERRQ(ierr); 132 133 ierr = VecGhostGetLocalForm(gx,&lx);CHKERRQ(ierr); 134 ierr = VecGetArray(lx,&array);CHKERRQ(ierr); 135 136 for (i=0; i<nlocal+nghost; i++) { 137 ierr = PetscSynchronizedPrintf(PETSC_COMM_WORLD,"%D %g\n",i,(double)PetscRealPart(array[i]));CHKERRQ(ierr); 138 } 139 ierr = VecRestoreArray(lx,&array);CHKERRQ(ierr); 140 ierr = PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT);CHKERRQ(ierr); 141 ierr = VecGhostRestoreLocalForm(gx,&lx);CHKERRQ(ierr); 142 } 143 144 ierr = VecDestroy(&gx);CHKERRQ(ierr); 145 146 if (flg) {ierr = PetscFree(tarray);CHKERRQ(ierr);} 147 ierr = PetscFinalize(); 148 return ierr; 149 } 150 151 /*TEST 152 153 test: 154 nsize: 2 155 156 test: 157 suffix: 2 158 nsize: 2 159 args: -allocate 160 output_file: output/ex9_1.out 161 162 test: 163 suffix: 3 164 nsize: 2 165 args: -vecmpisetghost 166 output_file: output/ex9_1.out 167 168 test: 169 suffix: 4 170 nsize: 2 171 args: -minvalues 172 output_file: output/ex9_2.out 173 requires: !complex 174 175 TEST*/ 176 177