Actual source code: ex7.c

petsc-3.7.1 2016-05-15
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  2: static char help[] = "Reads a PETSc matrix and vector from a file and solves a linear system.\n\
  3:  Tests inplace factorization for SeqBAIJ. Input parameters include\n\
  4:   -f0 <input_file> : first file to load (small system)\n\n";

  6: /*T
  7:    Concepts: KSP^solving a linear system
  8:    Concepts: PetscLog^profiling multiple stages of code;
  9:    Processors: n
 10: T*/

 12: /*
 13:   Include "petscksp.h" so that we can use KSP solvers.  Note that this file
 14:   automatically includes:
 15:      petscsys.h       - base PETSc routines   petscvec.h - vectors
 16:      petscmat.h - matrices
 17:      petscis.h     - index sets            petscksp.h - Krylov subspace methods
 18:      petscviewer.h - viewers               petscpc.h  - preconditioners
 19: */
 20: #include <petscksp.h>

 24: int main(int argc,char **args)
 25: {
 26:   KSP            ksp;             /* linear solver context */
 27:   Mat            A,B;                /* matrix */
 28:   Vec            x,b,u;          /* approx solution, RHS, exact solution */
 29:   PetscViewer    fd;               /* viewer */
 30:   char           file[2][PETSC_MAX_PATH_LEN];     /* input file name */
 32:   PetscInt       its;
 33:   PetscBool      flg;
 34:   PetscReal      norm;

 36:   PetscInitialize(&argc,&args,(char*)0,help);

 38:   /*
 39:      Determine files from which we read the two linear systems
 40:      (matrix and right-hand-side vector).
 41:   */
 42:   PetscOptionsGetString(NULL,NULL,"-f0",file[0],PETSC_MAX_PATH_LEN,&flg);
 43:   if (!flg) SETERRQ(PETSC_COMM_WORLD,1,"Must indicate binary file with the -f0 option");


 46:   /*
 47:        Open binary file.  Note that we use FILE_MODE_READ to indicate
 48:        reading from this file.
 49:   */
 50:   PetscViewerBinaryOpen(PETSC_COMM_WORLD,file[0],FILE_MODE_READ,&fd);

 52:   /*
 53:        Load the matrix and vector; then destroy the viewer.
 54:   */
 55:   MatCreate(PETSC_COMM_WORLD,&A);
 56:   MatSetType(A,MATSEQBAIJ);
 57:   MatLoad(A,fd);
 58:   MatConvert(A,MATSAME,MAT_INITIAL_MATRIX,&B);
 59:   VecCreate(PETSC_COMM_WORLD,&b);
 60:   VecLoad(b,fd);
 61:   PetscViewerDestroy(&fd);

 63:   /*
 64:        If the loaded matrix is larger than the vector (due to being padded
 65:        to match the block size of the system), then create a new padded vector.
 66:   */
 67:   {
 68:     PetscInt    m,n,j,mvec,start,end,idx;
 69:     Vec         tmp;
 70:     PetscScalar *bold;

 72:     /* Create a new vector b by padding the old one */
 73:     MatGetLocalSize(A,&m,&n);
 74:     VecCreate(PETSC_COMM_WORLD,&tmp);
 75:     VecSetSizes(tmp,m,PETSC_DECIDE);
 76:     VecSetFromOptions(tmp);
 77:     VecGetOwnershipRange(b,&start,&end);
 78:     VecGetLocalSize(b,&mvec);
 79:     VecGetArray(b,&bold);
 80:     for (j=0; j<mvec; j++) {
 81:       idx  = start+j;
 82:       VecSetValues(tmp,1,&idx,bold+j,INSERT_VALUES);
 83:     }
 84:     VecRestoreArray(b,&bold);
 85:     VecDestroy(&b);
 86:     VecAssemblyBegin(tmp);
 87:     VecAssemblyEnd(tmp);
 88:     b    = tmp;
 89:   }
 90:   VecDuplicate(b,&x);
 91:   VecDuplicate(b,&u);
 92:   VecSet(x,0.0);

 94:   /*
 95:       Create linear solver; set operators; set runtime options.
 96:   */
 97:   KSPCreate(PETSC_COMM_WORLD,&ksp);
 98:   KSPSetOperators(ksp,A,B);
 99:   KSPSetFromOptions(ksp);

101:   /*
102:        Here we explicitly call KSPSetUp() and KSPSetUpOnBlocks() to
103:        enable more precise profiling of setting up the preconditioner.
104:        These calls are optional, since both will be called within
105:        KSPSolve() if they haven't been called already.
106:   */
107:   KSPSetUp(ksp);
108:   KSPSetUpOnBlocks(ksp);
109:   KSPSolve(ksp,b,x);

111:   /*
112:             Check error, print output, free data structures.
113:             This stage is not profiled separately.
114:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

116:   /*
117:      Check error
118:   */
119:   MatMult(A,x,u);
120:   VecAXPY(u,-1.0,b);
121:   VecNorm(u,NORM_2,&norm);
122:   KSPGetIterationNumber(ksp,&its);
123:   PetscPrintf(PETSC_COMM_WORLD,"Number of iterations = %3D\n",its);
124:   PetscPrintf(PETSC_COMM_WORLD,"Residual norm = %g\n",(double)norm);

126:   /*
127:        Free work space.  All PETSc objects should be destroyed when they
128:        are no longer needed.
129:   */
130:   MatDestroy(&A);
131:   MatDestroy(&B);
132:   VecDestroy(&b);
133:   VecDestroy(&u); VecDestroy(&x);
134:   KSPDestroy(&ksp);


137:   PetscFinalize();
138:   return 0;
139: }