Actual source code: ex39.c

petsc-3.12.0 2019-09-29
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  1: /*
  2: mpiexec -n 8 ./ex39 -ksp_type fbcgs -ksp_rtol 1.e-6 -sub_ksp_type bcgs -sub_ksp_rtol 1.e-3 -pc_type bjacobi -ksp_converged_reason -ksp_monitor -n1 32 -n2 32 -n3 32

  4:   Contributed by Jie Chen for testing flexible BiCGStab algorithm
  5: */

  7: static char help[] = "Solves the PDE (in 3D) - laplacian(u) + gamma x dot grad(u) + beta u = 1\n\
  8: with zero Dirichlet condition. The discretization is standard centered\n\
  9: difference. Input parameters include:\n\
 10:   -n1        : number of mesh points in 1st dimension (default 32)\n\
 11:   -n2        : number of mesh points in 2nd dimension (default 32)\n\
 12:   -n3        : number of mesh points in 3nd dimension (default 32)\n\
 13:   -h         : spacing between mesh points (default 1/n1)\n\
 14:   -gamma     : gamma (default 4/h)\n\
 15:   -beta      : beta (default 0.01/h^2)\n\n";

 17:  #include <petscksp.h>
 18: int main(int argc,char **args)
 19: {
 20:   Vec            x,b,u;                 /* approx solution, RHS, working vector */
 21:   Mat            A;                     /* linear system matrix */
 22:   KSP            ksp;                   /* linear solver context */
 23:   PetscInt       n1, n2, n3;            /* parameters */
 24:   PetscReal      h, gamma, beta;        /* parameters */
 25:   PetscInt       i,j,k,Ii,J,Istart,Iend;
 27:   PetscScalar    v, co1, co2;

 29:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
 30:   n1 = 32;
 31:   n2 = 32;
 32:   n3 = 32;
 33:   PetscOptionsGetInt(NULL,NULL,"-n1",&n1,NULL);
 34:   PetscOptionsGetInt(NULL,NULL,"-n2",&n2,NULL);
 35:   PetscOptionsGetInt(NULL,NULL,"-n3",&n3,NULL);

 37:   h     = 1.0/n1;
 38:   gamma = 4.0/h;
 39:   beta  = 0.01/(h*h);
 40:   PetscOptionsGetReal(NULL,NULL,"-h",&h,NULL);
 41:   PetscOptionsGetReal(NULL,NULL,"-gamma",&gamma,NULL);
 42:   PetscOptionsGetReal(NULL,NULL,"-beta",&beta,NULL);

 44:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 45:          Compute the matrix and set right-hand-side vector.
 46:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 47:   MatCreate(PETSC_COMM_WORLD,&A);
 48:   MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n1*n2*n3,n1*n2*n3);
 49:   MatSetFromOptions(A);
 50:   MatMPIAIJSetPreallocation(A,7,NULL,7,NULL);
 51:   MatSeqAIJSetPreallocation(A,7,NULL);
 52:   MatSetUp(A);
 53:   MatGetOwnershipRange(A,&Istart,&Iend);

 55:   /*
 56:      Set matrix elements for the 3-D, seven-point stencil in parallel.
 57:       - Each processor needs to insert only elements that it owns
 58:         locally (but any non-local elements will be sent to the
 59:         appropriate processor during matrix assembly).
 60:       - Always specify global rows and columns of matrix entries.
 61:    */
 62:   co1  = gamma * h * h / 2.0;
 63:   co2  = beta * h * h;
 64:   for (Ii=Istart; Ii<Iend; Ii++) {
 65:     i = Ii/(n2*n3); j = (Ii - i*n2*n3)/n3; k = Ii - i*n2*n3 - j*n3;
 66:     if (i>0) {
 67:       J    = Ii - n2*n3;  v = -1.0 + co1*(PetscScalar)i;
 68:       MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);
 69:     }
 70:     if (i<n1-1) {
 71:       J    = Ii + n2*n3;  v = -1.0 + co1*(PetscScalar)i;
 72:       MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);
 73:     }
 74:     if (j>0) {
 75:       J    = Ii - n3;  v = -1.0 + co1*(PetscScalar)j;
 76:       MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);
 77:     }
 78:     if (j<n2-1) {
 79:       J    = Ii + n3;  v = -1.0 + co1*(PetscScalar)j;
 80:       MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);
 81:     }
 82:     if (k>0) {
 83:       J    = Ii - 1;  v = -1.0 + co1*(PetscScalar)k;
 84:       MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);
 85:     }
 86:     if (k<n3-1) {
 87:       J    = Ii + 1;  v = -1.0 + co1*(PetscScalar)k;
 88:       MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);
 89:     }
 90:     v    = 6.0 + co2;
 91:     MatSetValues(A,1,&Ii,1,&Ii,&v,INSERT_VALUES);
 92:   }
 93:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 94:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

 96:   /* Create parallel vectors and Set right-hand side. */
 97:   VecCreate(PETSC_COMM_WORLD,&b);
 98:   VecSetSizes(b,PETSC_DECIDE,n1*n2*n3);
 99:   VecSetFromOptions(b);
100:   VecDuplicate(b,&x);
101:   VecDuplicate(b,&u);
102:   VecSet(b,1.0);

104:   /* Create linear solver context */
105:   KSPCreate(PETSC_COMM_WORLD,&ksp);
106:   KSPSetOperators(ksp,A,A);
107:   KSPSetTolerances(ksp,1.e-6,1.e-50,PETSC_DEFAULT,200);
108:   KSPSetFromOptions(ksp);

110:   /* Solve the linear system */
111:   KSPSolve(ksp,b,x);

113:   /* Free work space.  */
114:   KSPDestroy(&ksp);
115:   VecDestroy(&u);  VecDestroy(&x);
116:   VecDestroy(&b);  MatDestroy(&A);
117:   PetscFinalize();
118:   return ierr;
119: }


122: /*TEST

124:    test:
125:       nsize: 8
126:       args: -ksp_type fbcgs -ksp_rtol 1.e-6 -sub_ksp_type bcgs -sub_ksp_rtol 1.e-3 -pc_type bjacobi -ksp_converged_reason -n1 32 -n2 32 -n3 32

128:    test:
129:       suffix: 2
130:       nsize: 8
131:       args: -ksp_type fbcgsr -ksp_rtol 1.e-6 -sub_ksp_type bcgs -sub_ksp_rtol 1.e-3 -pc_type bjacobi -ksp_converged_reason -n1 32 -n2 32 -n3 32
132:       output_file: output/ex39_1.out

134: TEST*/