Actual source code: ex47cu.cu
petsc-dev 2014-02-02
1: static char help[] = "Solves -Laplacian u - exp(u) = 0, 0 < x < 1 using GPU\n\n";
2: /*
3: Same as ex47.c except it also uses the GPU to evaluate the function
4: */
6: #include <petscdmda.h>
7: #include <petscsnes.h>
8: #include <petsccusp.h>
10: #include <thrust/for_each.h>
11: #include <thrust/tuple.h>
12: #include <thrust/iterator/constant_iterator.h>
13: #include <thrust/iterator/counting_iterator.h>
14: #include <thrust/iterator/zip_iterator.h>
16: extern PetscErrorCode ComputeFunction(SNES,Vec,Vec,void*), ComputeJacobian(SNES,Vec,Mat*,Mat*,MatStructure*,void*);
17: PetscBool useCUSP = PETSC_FALSE;
19: int main(int argc,char **argv)
20: {
21: SNES snes;
22: Vec x,f;
23: Mat J;
24: DM da;
26: char *tmp,typeName[256];
27: PetscBool flg;
29: PetscInitialize(&argc,&argv,(char*)0,help);
30: PetscOptionsGetString(NULL,"-dm_vec_type",typeName,256,&flg);
31: if (flg) {
32: PetscStrstr(typeName,"cusp",&tmp);
33: if (tmp) useCUSP = PETSC_TRUE;
34: }
36: DMDACreate1d(PETSC_COMM_WORLD,DMDA_BOUNDARY_NONE,-8,1,1,NULL,&da);
37: DMCreateGlobalVector(da,&x); VecDuplicate(x,&f);
38: DMSetMatType(da,MATAIJ);
39: DMCreateMatrix(da,&J);
41: SNESCreate(PETSC_COMM_WORLD,&snes);
42: SNESSetFunction(snes,f,ComputeFunction,da);
43: SNESSetJacobian(snes,J,J,ComputeJacobian,da);
44: SNESSetFromOptions(snes);
45: SNESSolve(snes,NULL,x);
47: MatDestroy(&J);
48: VecDestroy(&x);
49: VecDestroy(&f);
50: SNESDestroy(&snes);
51: DMDestroy(&da);
53: PetscFinalize();
54: return 0;
55: }
57: struct ApplyStencil
58: {
59: template <typename Tuple>
60: __host__ __device__
61: void operator()(Tuple t)
62: {
63: /* f = (2*x_i - x_(i+1) - x_(i-1))/h - h*exp(x_i) */
64: thrust::get<0>(t) = 1;
65: if ((thrust::get<4>(t) > 0) && (thrust::get<4>(t) < thrust::get<5>(t)-1)) {
66: thrust::get<0>(t) = (2.0*thrust::get<1>(t) - thrust::get<2>(t) - thrust::get<3>(t)) / (thrust::get<6>(t)) - (thrust::get<6>(t))*exp(thrust::get<1>(t));
67: } else if (thrust::get<4>(t) == 0) {
68: thrust::get<0>(t) = thrust::get<1>(t) / (thrust::get<6>(t));
69: } else if (thrust::get<4>(t) == thrust::get<5>(t)-1) {
70: thrust::get<0>(t) = thrust::get<1>(t) / (thrust::get<6>(t));
71: }
72: }
73: };
75: PetscErrorCode ComputeFunction(SNES snes,Vec x,Vec f,void *ctx)
76: {
77: PetscInt i,Mx,xs,xm,xstartshift,xendshift,fstart,lsize;
78: PetscScalar *xx,*ff,hx;
79: DM da = (DM) ctx;
80: Vec xlocal;
82: PetscMPIInt rank,size;
83: MPI_Comm comm;
84: cusp::array1d<PetscScalar,cusp::device_memory> *xarray,*farray;
86: DMDAGetInfo(da,PETSC_IGNORE,&Mx,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE);
87: hx = 1.0/(PetscReal)(Mx-1);
88: DMGetLocalVector(da,&xlocal);
89: DMGlobalToLocalBegin(da,x,INSERT_VALUES,xlocal);
90: DMGlobalToLocalEnd(da,x,INSERT_VALUES,xlocal);
92: if (useCUSP) {
93: VecCUSPGetArrayRead(xlocal,&xarray);
94: VecCUSPGetArrayWrite(f,&farray);
95: PetscObjectGetComm((PetscObject)da,&comm);
96: MPI_Comm_size(comm,&size);
97: MPI_Comm_rank(comm,&rank);
98: if (rank) xstartshift = 1;
99: else xstartshift = 0;
100: if (rank != size-1) xendshift = 1;
101: else xendshift = 0;
102: VecGetOwnershipRange(f,&fstart,NULL);
103: VecGetLocalSize(x,&lsize);
104: try {
105: thrust::for_each(
106: thrust::make_zip_iterator(
107: thrust::make_tuple(
108: farray->begin(),
109: xarray->begin()+xstartshift,
110: xarray->begin()+xstartshift + 1,
111: xarray->begin()+xstartshift - 1,
112: thrust::counting_iterator<int>(fstart),
113: thrust::constant_iterator<int>(Mx),
114: thrust::constant_iterator<PetscScalar>(hx))),
115: thrust::make_zip_iterator(
116: thrust::make_tuple(
117: farray->end(),
118: xarray->end()-xendshift,
119: xarray->end()-xendshift + 1,
120: xarray->end()-xendshift - 1,
121: thrust::counting_iterator<int>(fstart) + lsize,
122: thrust::constant_iterator<int>(Mx),
123: thrust::constant_iterator<PetscScalar>(hx))),
124: ApplyStencil());
125: }
126: catch (char *all) {
127: PetscPrintf(PETSC_COMM_WORLD, "Thrust is not working\n");
128: }
129: VecCUSPRestoreArrayRead(xlocal,&xarray);
130: VecCUSPRestoreArrayWrite(f,&farray);
131: } else {
132: DMDAVecGetArray(da,xlocal,&xx);
133: DMDAVecGetArray(da,f,&ff);
134: DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);
136: for (i=xs; i<xs+xm; i++) {
137: if (i == 0 || i == Mx-1) ff[i] = xx[i]/hx;
138: else ff[i] = (2.0*xx[i] - xx[i-1] - xx[i+1])/hx - hx*PetscExpScalar(xx[i]);
139: }
140: DMDAVecRestoreArray(da,xlocal,&xx);
141: DMDAVecRestoreArray(da,f,&ff);
142: }
143: DMRestoreLocalVector(da,&xlocal);
144: // VecView(x,0);printf("f\n");
145: // VecView(f,0);
146: return 0;
148: }
149: PetscErrorCode ComputeJacobian(SNES snes,Vec x,Mat *J,Mat *B,MatStructure *flag,void *ctx)
150: {
151: DM da = (DM) ctx;
152: PetscInt i,Mx,xm,xs;
153: PetscScalar hx,*xx;
154: Vec xlocal;
157: DMDAGetInfo(da,PETSC_IGNORE,&Mx,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE,PETSC_IGNORE);
158: hx = 1.0/(PetscReal)(Mx-1);
159: DMGetLocalVector(da,&xlocal);DMGlobalToLocalBegin(da,x,INSERT_VALUES,xlocal);
160: DMGlobalToLocalEnd(da,x,INSERT_VALUES,xlocal);
161: DMDAVecGetArray(da,xlocal,&xx);
162: DMDAGetCorners(da,&xs,NULL,NULL,&xm,NULL,NULL);
164: for (i=xs; i<xs+xm; i++) {
165: if (i == 0 || i == Mx-1) {
166: MatSetValue(*J,i,i,1.0/hx,INSERT_VALUES);
167: } else {
168: MatSetValue(*J,i,i-1,-1.0/hx,INSERT_VALUES);
169: MatSetValue(*J,i,i,2.0/hx - hx*PetscExpScalar(xx[i]),INSERT_VALUES);
170: MatSetValue(*J,i,i+1,-1.0/hx,INSERT_VALUES);
171: }
172: }
173: MatAssemblyBegin(*J,MAT_FINAL_ASSEMBLY);
174: MatAssemblyEnd(*J,MAT_FINAL_ASSEMBLY);
175: *flag = SAME_NONZERO_PATTERN;
176: DMDAVecRestoreArray(da,xlocal,&xx);
177: DMRestoreLocalVector(da,&xlocal);
178: return 0;
179: }