Actual source code: ex28.c


  3: static char help[] = "Solves 1D wave equation using multigrid.\n\n";

 5:  #include petscda.h
 6:  #include petscksp.h
 7:  #include petscdmmg.h


 15: int main(int argc,char **argv)
 16: {
 18:   PetscInt       i;
 19:   DMMG           *dmmg;
 20:   PetscScalar    mone = -1.0;
 21:   PetscReal      norm;
 22:   DA             da;

 24:   PetscInitialize(&argc,&argv,(char *)0,help);

 26:   DMMGCreate(PETSC_COMM_WORLD,3,PETSC_NULL,&dmmg);
 27:   DACreate1d(PETSC_COMM_WORLD,DA_XPERIODIC,-3,2,1,0,&da);
 28:   DMMGSetDM(dmmg,(DM)da);
 29:   DADestroy(da);

 31:   DMMGSetKSP(dmmg,ComputeRHS,ComputeJacobian);

 33:   ComputeInitialSolution(dmmg);

 35:   VecView(DMMGGetx(dmmg),PETSC_VIEWER_DRAW_WORLD);
 36:   for (i=0; i<1000; i++) {
 37:     DMMGSolve(dmmg);
 38:     VecView(DMMGGetx(dmmg),PETSC_VIEWER_DRAW_WORLD);
 39:   }
 40:   MatMult(DMMGGetJ(dmmg),DMMGGetx(dmmg),DMMGGetr(dmmg));
 41:   VecAXPY(DMMGGetr(dmmg),mone,DMMGGetRHS(dmmg));
 42:   VecNorm(DMMGGetr(dmmg),NORM_2,&norm);
 43:   /* PetscPrintf(PETSC_COMM_WORLD,"Residual norm %g\n",norm); */

 45:   DMMGDestroy(dmmg);
 46:   PetscFinalize();

 48:   return 0;
 49: }

 53: PetscErrorCode ComputeInitialSolution(DMMG *dmmg)
 54: {
 56:   PetscInt       mx,col[2],xs,xm,i;
 57:   PetscScalar    Hx,val[2];
 58:   Vec            x = DMMGGetx(dmmg);

 61:   DAGetInfo(DMMGGetDA(dmmg),0,&mx,0,0,0,0,0,0,0,0,0);
 62:   Hx = 2.0*PETSC_PI / (PetscReal)(mx);
 63:   DAGetCorners(DMMGGetDA(dmmg),&xs,0,0,&xm,0,0);
 64: 
 65:   for(i=xs; i<xs+xm; i++){
 66:     col[0] = 2*i; col[1] = 2*i + 1;
 67:     val[0] = val[1] = PetscSinScalar(((PetscScalar)i)*Hx);
 68:     VecSetValues(x,2,col,val,INSERT_VALUES);
 69:   }
 70:   VecAssemblyBegin(x);
 71:   VecAssemblyEnd(x);
 72:   return(0);
 73: }
 74: 
 77: PetscErrorCode ComputeRHS(DMMG dmmg,Vec b)
 78: {
 80:   PetscInt       mx;
 81:   PetscScalar    h;

 84:   DAGetInfo((DA)dmmg->dm,0,&mx,0,0,0,0,0,0,0,0,0);
 85:   h    = 2.0*PETSC_PI/((mx));
 86:   VecCopy(dmmg->x,b);
 87:   VecScale(b,h);
 88:   return(0);
 89: }

 93: PetscErrorCode ComputeJacobian(DMMG dmmg,Mat jac)
 94: {
 95:   DA             da = (DA)dmmg->dm;
 97:   PetscInt       i,mx,xm,xs;
 98:   PetscScalar    v[7],Hx;
 99:   MatStencil     row,col[7];
100:   PetscScalar    lambda;

102:   PetscMemzero(col,7*sizeof(MatStencil));
103:   DAGetInfo(da,0,&mx,0,0,0,0,0,0,0,0,0);
104:   Hx = 2.0*PETSC_PI / (PetscReal)(mx);
105:   DAGetCorners(da,&xs,0,0,&xm,0,0);
106:   lambda = 2.0*Hx;
107:   for(i=xs; i<xs+xm; i++){
108:     row.i = i; row.j = 0; row.k = 0; row.c = 0;
109:     v[0] = Hx;     col[0].i = i;   col[0].c = 0;
110:     v[1] = lambda; col[1].i = i-1;   col[1].c = 1;
111:     v[2] = -lambda;col[2].i = i+1; col[2].c = 1;
112:     MatSetValuesStencil(jac,1,&row,3,col,v,INSERT_VALUES);

114:     row.i = i; row.j = 0; row.k = 0; row.c = 1;
115:     v[0] = lambda; col[0].i = i-1;   col[0].c = 0;
116:     v[1] = Hx;     col[1].i = i;   col[1].c = 1;
117:     v[2] = -lambda;col[2].i = i+1; col[2].c = 0;
118:     MatSetValuesStencil(jac,1,&row,3,col,v,INSERT_VALUES);
119:   }
120:   MatAssemblyBegin(jac,MAT_FINAL_ASSEMBLY);
121:   MatAssemblyEnd(jac,MAT_FINAL_ASSEMBLY);
122:   MatView(jac,PETSC_VIEWER_BINARY_(PETSC_COMM_SELF));
123:   return 0;
124: }