Actual source code: ex7.c

petsc-3.8.3 2017-12-09
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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>

 22: int main(int argc,char **args)
 23: {
 24:   KSP            ksp;             /* linear solver context */
 25:   Mat            A,B;                /* matrix */
 26:   Vec            x,b,u;          /* approx solution, RHS, exact solution */
 27:   PetscViewer    fd;               /* viewer */
 28:   char           file[2][PETSC_MAX_PATH_LEN];     /* input file name */
 30:   PetscInt       its;
 31:   PetscBool      flg;
 32:   PetscReal      norm;

 34:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
 35:   /*
 36:      Determine files from which we read the two linear systems
 37:      (matrix and right-hand-side vector).
 38:   */
 39:   PetscOptionsGetString(NULL,NULL,"-f0",file[0],PETSC_MAX_PATH_LEN,&flg);
 40:   if (!flg) SETERRQ(PETSC_COMM_WORLD,1,"Must indicate binary file with the -f0 option");


 43:   /*
 44:        Open binary file.  Note that we use FILE_MODE_READ to indicate
 45:        reading from this file.
 46:   */
 47:   PetscViewerBinaryOpen(PETSC_COMM_WORLD,file[0],FILE_MODE_READ,&fd);

 49:   /*
 50:        Load the matrix and vector; then destroy the viewer.
 51:   */
 52:   MatCreate(PETSC_COMM_WORLD,&A);
 53:   MatSetType(A,MATSEQBAIJ);
 54:   MatLoad(A,fd);
 55:   MatConvert(A,MATSAME,MAT_INITIAL_MATRIX,&B);
 56:   VecCreate(PETSC_COMM_WORLD,&b);
 57:   VecLoad(b,fd);
 58:   PetscViewerDestroy(&fd);

 60:   /*
 61:        If the loaded matrix is larger than the vector (due to being padded
 62:        to match the block size of the system), then create a new padded vector.
 63:   */
 64:   {
 65:     PetscInt    m,n,j,mvec,start,end,idx;
 66:     Vec         tmp;
 67:     PetscScalar *bold;

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

 91:   /*
 92:       Create linear solver; set operators; set runtime options.
 93:   */
 94:   KSPCreate(PETSC_COMM_WORLD,&ksp);
 95:   KSPSetOperators(ksp,A,B);
 96:   KSPSetFromOptions(ksp);

 98:   /*
 99:        Here we explicitly call KSPSetUp() and KSPSetUpOnBlocks() to
100:        enable more precise profiling of setting up the preconditioner.
101:        These calls are optional, since both will be called within
102:        KSPSolve() if they haven't been called already.
103:   */
104:   KSPSetUp(ksp);
105:   KSPSetUpOnBlocks(ksp);
106:   KSPSolve(ksp,b,x);

108:   /*
109:             Check error, print output, free data structures.
110:             This stage is not profiled separately.
111:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

113:   /*
114:      Check error
115:   */
116:   MatMult(A,x,u);
117:   VecAXPY(u,-1.0,b);
118:   VecNorm(u,NORM_2,&norm);
119:   KSPGetIterationNumber(ksp,&its);
120:   PetscPrintf(PETSC_COMM_WORLD,"Number of iterations = %3D\n",its);
121:   PetscPrintf(PETSC_COMM_WORLD,"Residual norm = %g\n",(double)norm);

123:   /*
124:        Free work space.  All PETSc objects should be destroyed when they
125:        are no longer needed.
126:   */
127:   MatDestroy(&A);
128:   MatDestroy(&B);
129:   VecDestroy(&b);
130:   VecDestroy(&u); VecDestroy(&x);
131:   KSPDestroy(&ksp);


134:   PetscFinalize();
135:   return ierr;
136: }