Actual source code: ex29.c

petsc-3.13.4 2020-08-01
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  2: static char help[] ="Tests ML interface. Modified from ~src/ksp/ksp/tests/ex19.c \n\
  3:   -mx <xg>, where <xg> = number of grid points in the x-direction\n\
  4:   -my <yg>, where <yg> = number of grid points in the y-direction\n\
  5:   -Nx <npx>, where <npx> = number of processors in the x-direction\n\
  6:   -Ny <npy>, where <npy> = number of processors in the y-direction\n\n";

  8: /*
  9:     This problem is modeled by
 10:     the partial differential equation

 12:             -Laplacian u  = g,  0 < x,y < 1,

 14:     with boundary conditions

 16:              u = 0  for  x = 0, x = 1, y = 0, y = 1.

 18:     A finite difference approximation with the usual 5-point stencil
 19:     is used to discretize the boundary value problem to obtain a nonlinear
 20:     system of equations.

 22:     Usage: ./ex29 -ksp_type gmres -ksp_monitor
 23:            -pc_mg_type <multiplicative> (one of) additive multiplicative full kascade
 24:            -mg_coarse_ksp_max_it 10 -mg_levels_3_ksp_max_it 10 -mg_levels_2_ksp_max_it 10
 25:            -mg_levels_1_ksp_max_it 10 -mg_fine_ksp_max_it 10
 26: */

 28:  #include <petscksp.h>
 29:  #include <petscdm.h>
 30:  #include <petscdmda.h>

 32: /* User-defined Section 1.5 Writing Application Codes with PETSc contexts */
 33: typedef struct {
 34:   PetscInt mx,my;              /* number grid points in x and y direction */
 35:   Vec      localX,localF;      /* local vectors with ghost region */
 36:   DM       da;
 37:   Vec      x,b,r;              /* global vectors */
 38:   Mat      J;                  /* Jacobian on grid */
 39:   Mat      A,P,R;
 40:   KSP      ksp;
 41: } GridCtx;
 42: extern int FormJacobian_Grid(GridCtx*,Mat*);

 44: int main(int argc,char **argv)
 45: {
 47:   PetscInt       its,n,Nx=PETSC_DECIDE,Ny=PETSC_DECIDE,nlocal,i;
 48:   PetscMPIInt    size;
 49:   PC             pc;
 50:   PetscInt       mx,my;
 51:   Mat            A;
 52:   GridCtx        fine_ctx;
 53:   KSP            ksp;
 54:   PetscBool      flg;

 56:   PetscInitialize(&argc,&argv,NULL,help);if (ierr) return ierr;
 57:   /* set up discretization matrix for fine grid */
 58:   /* ML requires input of fine-grid matrix. It determines nlevels. */
 59:   fine_ctx.mx = 9; fine_ctx.my = 9;
 60:   PetscOptionsGetInt(NULL,NULL,"-mx",&mx,&flg);
 61:   if (flg) fine_ctx.mx = mx;
 62:   PetscOptionsGetInt(NULL,NULL,"-my",&my,&flg);
 63:   if (flg) fine_ctx.my = my;
 64:   PetscPrintf(PETSC_COMM_WORLD,"Fine grid size %D by %D\n",fine_ctx.mx,fine_ctx.my);
 65:   n    = fine_ctx.mx*fine_ctx.my;

 67:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 68:   PetscOptionsGetInt(NULL,NULL,"-Nx",&Nx,NULL);
 69:   PetscOptionsGetInt(NULL,NULL,"-Ny",&Ny,NULL);

 71:   DMDACreate2d(PETSC_COMM_WORLD, DM_BOUNDARY_NONE, DM_BOUNDARY_NONE,DMDA_STENCIL_STAR,fine_ctx.mx,fine_ctx.my,Nx,Ny,1,1,NULL,NULL,&fine_ctx.da);
 72:   DMSetFromOptions(fine_ctx.da);
 73:   DMSetUp(fine_ctx.da);
 74:   DMCreateGlobalVector(fine_ctx.da,&fine_ctx.x);
 75:   VecDuplicate(fine_ctx.x,&fine_ctx.b);
 76:   VecGetLocalSize(fine_ctx.x,&nlocal);
 77:   DMCreateLocalVector(fine_ctx.da,&fine_ctx.localX);
 78:   VecDuplicate(fine_ctx.localX,&fine_ctx.localF);
 79:   MatCreateAIJ(PETSC_COMM_WORLD,nlocal,nlocal,n,n,5,NULL,3,NULL,&A);
 80:   FormJacobian_Grid(&fine_ctx,&A);

 82:   /* create linear solver */
 83:   KSPCreate(PETSC_COMM_WORLD,&ksp);
 84:   KSPGetPC(ksp,&pc);
 85:   PCSetType(pc,PCML);

 87:   /* set options, then solve system */
 88:   KSPSetFromOptions(ksp); /* calls PCSetFromOptions_MG/ML */

 90:   for (i=0; i<3; i++) {
 91:     if (i<2) { 
 92:       /* set values for rhs vector */
 93:       VecSet(fine_ctx.b,i+1.0);
 94:       /* modify A */
 95:       MatShift(A,1.0);
 96:       MatScale(A,2.0);
 97:       KSPSetOperators(ksp,A,A);
 98:     } else {  /* test SAME_NONZERO_PATTERN */
 99:       KSPSetOperators(ksp,A,A);
100:     }
101:     KSPSolve(ksp,fine_ctx.b,fine_ctx.x);
102:     KSPGetIterationNumber(ksp,&its);
103:     if (its > 6) {
104:       PetscPrintf(PETSC_COMM_WORLD,"Warning: Number of iterations = %D greater than expected\n",its);
105:     }
106:   }

108:   /* free data structures */
109:   VecDestroy(&fine_ctx.x);
110:   VecDestroy(&fine_ctx.b);
111:   DMDestroy(&fine_ctx.da);
112:   VecDestroy(&fine_ctx.localX);
113:   VecDestroy(&fine_ctx.localF);
114:   MatDestroy(&A);
115:   KSPDestroy(&ksp);
116:   PetscFinalize();
117:   return ierr;
118: }

120: int FormJacobian_Grid(GridCtx *grid,Mat *J)
121: {
122:   Mat                    jac = *J;
123:   PetscErrorCode         ierr;
124:   PetscInt               i,j,row,mx,my,xs,ys,xm,ym,Xs,Ys,Xm,Ym,col[5];
125:   PetscInt               grow;
126:   const PetscInt         *ltog;
127:   PetscScalar            two = 2.0,one = 1.0,v[5],hx,hy,hxdhy,hydhx,value;
128:   ISLocalToGlobalMapping ltogm;

130:   mx    = grid->mx;               my = grid->my;
131:   hx    = one/(PetscReal)(mx-1);  hy = one/(PetscReal)(my-1);
132:   hxdhy = hx/hy;               hydhx = hy/hx;

134:   /* Get ghost points */
135:   DMDAGetCorners(grid->da,&xs,&ys,0,&xm,&ym,0);
136:   DMDAGetGhostCorners(grid->da,&Xs,&Ys,0,&Xm,&Ym,0);
137:   DMGetLocalToGlobalMapping(grid->da,&ltogm);
138:   ISLocalToGlobalMappingGetIndices(ltogm,&ltog);

140:   /* Evaluate Jacobian of function */
141:   for (j=ys; j<ys+ym; j++) {
142:     row = (j - Ys)*Xm + xs - Xs - 1;
143:     for (i=xs; i<xs+xm; i++) {
144:       row++;
145:       grow = ltog[row];
146:       if (i > 0 && i < mx-1 && j > 0 && j < my-1) {
147:         v[0] = -hxdhy; col[0] = ltog[row - Xm];
148:         v[1] = -hydhx; col[1] = ltog[row - 1];
149:         v[2] = two*(hydhx + hxdhy); col[2] = grow;
150:         v[3] = -hydhx; col[3] = ltog[row + 1];
151:         v[4] = -hxdhy; col[4] = ltog[row + Xm];
152:         MatSetValues(jac,1,&grow,5,col,v,INSERT_VALUES);
153:       } else if ((i > 0 && i < mx-1) || (j > 0 && j < my-1)) {
154:         value = .5*two*(hydhx + hxdhy);
155:         MatSetValues(jac,1,&grow,1,&grow,&value,INSERT_VALUES);
156:       } else {
157:         value = .25*two*(hydhx + hxdhy);
158:         MatSetValues(jac,1,&grow,1,&grow,&value,INSERT_VALUES);
159:       }
160:     }
161:   }
162:   ISLocalToGlobalMappingRestoreIndices(ltogm,&ltog);
163:   MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY);
164:   MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY);
165:   return 0;
166: }

168: /*TEST

170:     test:
171:       output_file: output/ex29.out
172:       args: -mat_no_inode
173:       requires: ml

175:     test:
176:       suffix: 2
177:       nsize: 3
178:       requires: ml

180: TEST*/