Actual source code: ex45.c
petsc-3.4.5 2014-06-29
2: /*
3: Laplacian in 3D. Modeled by the partial differential equation
5: - Laplacian u = 1,0 < x,y,z < 1,
7: with boundary conditions
9: u = 1 for x = 0, x = 1, y = 0, y = 1, z = 0, z = 1.
11: This uses multigrid to solve the linear system
13: See src/snes/examples/tutorials/ex50.c
15: Can also be run with -pc_type exotic -ksp_type fgmres
17: */
19: static char help[] = "Solves 3D Laplacian using multigrid.\n\n";
21: #include <petscksp.h>
22: #include <petscdmda.h>
24: extern PetscErrorCode ComputeMatrix(KSP,Mat,Mat,MatStructure*,void*);
25: extern PetscErrorCode ComputeRHS(KSP,Vec,void*);
26: extern PetscErrorCode ComputeInitialGuess(KSP,Vec,void*);
30: int main(int argc,char **argv)
31: {
33: KSP ksp;
34: PetscReal norm;
35: DM da;
36: Vec x,b,r;
37: Mat A;
39: PetscInitialize(&argc,&argv,(char*)0,help);
41: KSPCreate(PETSC_COMM_WORLD,&ksp);
42: DMDACreate3d(PETSC_COMM_WORLD,DMDA_BOUNDARY_NONE,DMDA_BOUNDARY_NONE,DMDA_BOUNDARY_NONE,DMDA_STENCIL_STAR,-7,-7,-7,PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE,1,1,0,0,0,&da);
43: KSPSetDM(ksp,da);
44: KSPSetComputeInitialGuess(ksp,ComputeInitialGuess,NULL);
45: KSPSetComputeRHS(ksp,ComputeRHS,NULL);
46: KSPSetComputeOperators(ksp,ComputeMatrix,NULL);
47: DMDestroy(&da);
49: KSPSetFromOptions(ksp);
50: KSPSolve(ksp,NULL,NULL);
51: KSPGetSolution(ksp,&x);
52: KSPGetRhs(ksp,&b);
53: VecDuplicate(b,&r);
54: KSPGetOperators(ksp,&A,NULL,NULL);
56: MatMult(A,x,r);
57: VecAXPY(r,-1.0,b);
58: VecNorm(r,NORM_2,&norm);
59: PetscPrintf(PETSC_COMM_WORLD,"Residual norm %G\n",norm);
61: VecDestroy(&r);
62: KSPDestroy(&ksp);
63: PetscFinalize();
65: return 0;
66: }
70: PetscErrorCode ComputeRHS(KSP ksp,Vec b,void *ctx)
71: {
73: PetscInt i,j,k,mx,my,mz,xm,ym,zm,xs,ys,zs;
74: DM dm;
75: PetscScalar Hx,Hy,Hz,HxHydHz,HyHzdHx,HxHzdHy;
76: PetscScalar ***barray;
79: KSPGetDM(ksp,&dm);
80: DMDAGetInfo(dm,0,&mx,&my,&mz,0,0,0,0,0,0,0,0,0);
81: Hx = 1.0 / (PetscReal)(mx-1); Hy = 1.0 / (PetscReal)(my-1); Hz = 1.0 / (PetscReal)(mz-1);
82: HxHydHz = Hx*Hy/Hz; HxHzdHy = Hx*Hz/Hy; HyHzdHx = Hy*Hz/Hx;
83: DMDAGetCorners(dm,&xs,&ys,&zs,&xm,&ym,&zm);
84: DMDAVecGetArray(dm,b,&barray);
86: for (k=zs; k<zs+zm; k++) {
87: for (j=ys; j<ys+ym; j++) {
88: for (i=xs; i<xs+xm; i++) {
89: if (i==0 || j==0 || k==0 || i==mx-1 || j==my-1 || k==mz-1) {
90: barray[k][j][i] = 2.0*(HxHydHz + HxHzdHy + HyHzdHx);
91: } else {
92: barray[k][j][i] = Hx*Hy*Hz;
93: }
94: }
95: }
96: }
97: DMDAVecRestoreArray(dm,b,&barray);
98: return(0);
99: }
103: PetscErrorCode ComputeInitialGuess(KSP ksp,Vec b,void *ctx)
104: {
108: VecSet(b,0);
109: return(0);
110: }
114: PetscErrorCode ComputeMatrix(KSP ksp,Mat jac,Mat B,MatStructure *stflg,void *ctx)
115: {
116: DM da;
118: PetscInt i,j,k,mx,my,mz,xm,ym,zm,xs,ys,zs;
119: PetscScalar v[7],Hx,Hy,Hz,HxHydHz,HyHzdHx,HxHzdHy;
120: MatStencil row,col[7];
123: KSPGetDM(ksp,&da);
124: DMDAGetInfo(da,0,&mx,&my,&mz,0,0,0,0,0,0,0,0,0);
125: Hx = 1.0 / (PetscReal)(mx-1); Hy = 1.0 / (PetscReal)(my-1); Hz = 1.0 / (PetscReal)(mz-1);
126: HxHydHz = Hx*Hy/Hz; HxHzdHy = Hx*Hz/Hy; HyHzdHx = Hy*Hz/Hx;
127: DMDAGetCorners(da,&xs,&ys,&zs,&xm,&ym,&zm);
129: for (k=zs; k<zs+zm; k++) {
130: for (j=ys; j<ys+ym; j++) {
131: for (i=xs; i<xs+xm; i++) {
132: row.i = i; row.j = j; row.k = k;
133: if (i==0 || j==0 || k==0 || i==mx-1 || j==my-1 || k==mz-1) {
134: v[0] = 2.0*(HxHydHz + HxHzdHy + HyHzdHx);
135: MatSetValuesStencil(B,1,&row,1,&row,v,INSERT_VALUES);
136: } else {
137: v[0] = -HxHydHz;col[0].i = i; col[0].j = j; col[0].k = k-1;
138: v[1] = -HxHzdHy;col[1].i = i; col[1].j = j-1; col[1].k = k;
139: v[2] = -HyHzdHx;col[2].i = i-1; col[2].j = j; col[2].k = k;
140: v[3] = 2.0*(HxHydHz + HxHzdHy + HyHzdHx);col[3].i = row.i; col[3].j = row.j; col[3].k = row.k;
141: v[4] = -HyHzdHx;col[4].i = i+1; col[4].j = j; col[4].k = k;
142: v[5] = -HxHzdHy;col[5].i = i; col[5].j = j+1; col[5].k = k;
143: v[6] = -HxHydHz;col[6].i = i; col[6].j = j; col[6].k = k+1;
144: MatSetValuesStencil(B,1,&row,7,col,v,INSERT_VALUES);
145: }
146: }
147: }
148: }
149: MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);
150: MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);
151: *stflg = SAME_NONZERO_PATTERN;
152: return(0);
153: }