Actual source code: ex28.c
petsc-3.12.4 2020-02-04
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      2: static char help[] = "Test procedural KSPSetFromOptions() or at runtime; Test PCREDUNDANT.\n\n";

      4: /*T
      5:    Concepts: KSP^basic parallel example;
      6:    Processors: n
      7: T*/
      8:  #include <petscksp.h>

     10: int main(int argc,char **args)
     11: {
     12:   Vec            x, b, u;     /* approx solution, RHS, exact solution */
     13:   Mat            A;           /* linear system matrix */
     14:   KSP            ksp;         /* linear solver context */
     15:   PC             pc;          /* preconditioner context */
     16:   PetscReal      norm;        /* norm of solution error */
     18:   PetscInt       i,n = 10,col[3],its,rstart,rend,nlocal;
     19:   PetscScalar    one = 1.0,value[3];
     20:   PetscBool      TEST_PROCEDURAL=PETSC_FALSE;

     22:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
     23:   PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);
     24:   PetscOptionsGetBool(NULL,NULL,"-procedural",&TEST_PROCEDURAL,NULL);

     26:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     27:          Compute the matrix and right-hand-side vector that define
     28:          the linear system, Ax = b.
     29:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     31:   /*
     32:      Create vectors.  Note that we form 1 vector from scratch and
     33:      then duplicate as needed. For this simple case let PETSc decide how
     34:      many elements of the vector are stored on each processor. The second
     35:      argument to VecSetSizes() below causes PETSc to decide.
     36:   */
     37:   VecCreate(PETSC_COMM_WORLD,&x);
     38:   VecSetSizes(x,PETSC_DECIDE,n);
     39:   VecSetFromOptions(x);
     40:   VecDuplicate(x,&b);
     41:   VecDuplicate(x,&u);

     43:   /* Identify the starting and ending mesh points on each
     44:      processor for the interior part of the mesh. We let PETSc decide
     45:      above. */

     47:   VecGetOwnershipRange(x,&rstart,&rend);
     48:   VecGetLocalSize(x,&nlocal);

     50:   /* Create a tridiagonal matrix. See ../tutorials/ex23.c */
     51:   MatCreate(PETSC_COMM_WORLD,&A);
     52:   MatSetSizes(A,nlocal,nlocal,n,n);
     53:   MatSetFromOptions(A);
     54:   MatSetUp(A);
     55:   /* Assemble matrix */
     56:   if (!rstart) {
     57:     rstart = 1;
     58:     i      = 0; col[0] = 0; col[1] = 1; value[0] = 2.0; value[1] = -1.0;
     59:     MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
     60:   }
     61:   if (rend == n) {
     62:     rend = n-1;
     63:     i    = n-1; col[0] = n-2; col[1] = n-1; value[0] = -1.0; value[1] = 2.0;
     64:     MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);
     65:   }

     67:   /* Set entries corresponding to the mesh interior */
     68:   value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
     69:   for (i=rstart; i<rend; i++) {
     70:     col[0] = i-1; col[1] = i; col[2] = i+1;
     71:     MatSetValues(A,1,&i,3,col,value,INSERT_VALUES);
     72:   }
     73:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
     74:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

     76:   /* Set exact solution; then compute right-hand-side vector. */
     77:   VecSet(u,one);
     78:   MatMult(A,u,b);

     80:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     81:                 Create the linear solver and set various options
     82:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
     83:   KSPCreate(PETSC_COMM_WORLD,&ksp);
     84:   KSPSetOperators(ksp,A,A);

     86:   /*
     87:      Set linear solver defaults for this problem (optional).
     88:      - By extracting the KSP and PC contexts from the KSP context,
     89:        we can then directly call any KSP and PC routines to set
     90:        various options.
     91:      - The following statements are optional; all of these
     92:        parameters could alternatively be specified at runtime via
     93:        KSPSetFromOptions();
     94:   */
     95:   if (TEST_PROCEDURAL) {
     96:     /* Example of runtime options: '-pc_redundant_number 3 -redundant_ksp_type gmres -redundant_pc_type bjacobi' */
     97:     PetscMPIInt size,rank,subsize;
     98:     Mat         A_redundant;
     99:     KSP         innerksp;
    100:     PC          innerpc;
    101:     MPI_Comm    subcomm;

    103:     KSPGetPC(ksp,&pc);
    104:     PCSetType(pc,PCREDUNDANT);
    105:     MPI_Comm_size(PETSC_COMM_WORLD,&size);
    106:     MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
    107:     if (size < 3) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_ARG_SIZ, "Num of processes %d must greater than 2",size);
    108:     PCRedundantSetNumber(pc,size-2);
    109:     KSPSetFromOptions(ksp);

    111:     /* Get subcommunicator and redundant matrix */
    112:     KSPSetUp(ksp);
    113:     PCRedundantGetKSP(pc,&innerksp);
    114:     KSPGetPC(innerksp,&innerpc);
    115:     PCGetOperators(innerpc,NULL,&A_redundant);
    116:     PetscObjectGetComm((PetscObject)A_redundant,&subcomm);
    117:     MPI_Comm_size(subcomm,&subsize);
    118:     if (subsize==1 && !rank) {
    119:       PetscPrintf(PETSC_COMM_SELF,"A_redundant:\n");
    120:       MatView(A_redundant,PETSC_VIEWER_STDOUT_SELF);
    121:     }
    122:   } else {
    123:     KSPSetFromOptions(ksp);
    124:   }
    125:
    126:   /*  Solve linear system */
    127:   KSPSolve(ksp,b,x);

    129:   /* Check the error */
    130:   VecAXPY(x,-1.0,u);
    131:   VecNorm(x,NORM_2,&norm);
    132:   KSPGetIterationNumber(ksp,&its);
    133:   PetscPrintf(PETSC_COMM_WORLD,"Norm of error %g, Iterations %D\n",(double)norm,its);

    135:   /* Free work space. */
    136:   VecDestroy(&x); VecDestroy(&u);
    137:   VecDestroy(&b); MatDestroy(&A);
    138:   KSPDestroy(&ksp);
    139:   PetscFinalize();
    140:   return ierr;
    141: }

    143: /*TEST

    145:     test:
    146:       nsize: 3
    147:       output_file: output/ex28.out

    149:     test:
    150:       suffix: 2
    151:       args:  -procedural -pc_redundant_number 3 -redundant_ksp_type gmres -redundant_pc_type bjacobi
    152:       nsize: 3

    154:     test:
    155:       suffix: 3
    156:       args:  -procedural -pc_redundant_number 3 -redundant_ksp_type gmres -redundant_pc_type bjacobi
    157:       nsize: 5

    159: TEST*/