Example #1
0
int main( int argc, char **argv )
{
  PetscErrorCode ierr;
  Mat         	 A;		  /* Grcar matrix */
  SVD            svd;             /* singular value solver context */
  PetscInt    	 N=30, Istart, Iend, i, col[5], nconv1, nconv2;
  PetscScalar 	 value[] = { -1, 1, 1, 1, 1 };
  PetscReal   	 sigma_1, sigma_n;

  SlepcInitialize(&argc,&argv,(char*)0,help);

  ierr = PetscOptionsGetInt(PETSC_NULL,"-n",&N,PETSC_NULL);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD,"\nEstimate the condition number of a Grcar matrix, n=%d\n\n",N);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
        Generate the matrix 
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
  ierr = MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N);CHKERRQ(ierr);
  ierr = MatSetFromOptions(A);CHKERRQ(ierr);

  ierr = MatGetOwnershipRange(A,&Istart,&Iend);CHKERRQ(ierr);
  for( i=Istart; i<Iend; i++ ) {
    col[0]=i-1; col[1]=i; col[2]=i+1; col[3]=i+2; col[4]=i+3;
    if (i==0) {
      ierr = MatSetValues(A,1,&i,4,col+1,value+1,INSERT_VALUES);CHKERRQ(ierr);
    }
    else {
      ierr = MatSetValues(A,1,&i,PetscMin(5,N-i+1),col,value,INSERT_VALUES);CHKERRQ(ierr);
    }
  }

  ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
  ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
             Create the singular value solver and set the solution method
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  /* 
     Create singular value context
  */
  ierr = SVDCreate(PETSC_COMM_WORLD,&svd);CHKERRQ(ierr);

  /* 
     Set operator
  */
  ierr = SVDSetOperator(svd,A);CHKERRQ(ierr);

  /*
     Set solver parameters at runtime
  */
  ierr = SVDSetFromOptions(svd);CHKERRQ(ierr);
  ierr = SVDSetDimensions(svd,1,PETSC_IGNORE,PETSC_IGNORE);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
                      Solve the eigensystem
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  /*
     First request an eigenvalue from one end of the spectrum
  */
  ierr = SVDSetWhichSingularTriplets(svd,SVD_LARGEST);CHKERRQ(ierr);
  ierr = SVDSolve(svd);CHKERRQ(ierr);
  /* 
     Get number of converged singular values
  */
  ierr = SVDGetConverged(svd,&nconv1);CHKERRQ(ierr);
  /* 
     Get converged singular values: largest singular value is stored in sigma_1.
     In this example, we are not interested in the singular vectors
  */
  if (nconv1 > 0) {
    ierr = SVDGetSingularTriplet(svd,0,&sigma_1,PETSC_NULL,PETSC_NULL);CHKERRQ(ierr);
  } else {
    ierr = PetscPrintf(PETSC_COMM_WORLD," Unable to compute large singular value!\n\n");CHKERRQ(ierr);
  } 

  /*
     Request an eigenvalue from the other end of the spectrum
  */
  ierr = SVDSetWhichSingularTriplets(svd,SVD_SMALLEST);CHKERRQ(ierr);
  ierr = SVDSolve(svd);CHKERRQ(ierr);
  /* 
     Get number of converged eigenpairs
  */
  ierr = SVDGetConverged(svd,&nconv2);CHKERRQ(ierr);
  /* 
     Get converged singular values: smallest singular value is stored in sigma_n. 
     As before, we are not interested in the singular vectors
  */
  if (nconv2 > 0) {
    ierr = SVDGetSingularTriplet(svd,0,&sigma_n,PETSC_NULL,PETSC_NULL);CHKERRQ(ierr);
  } else {
    ierr = PetscPrintf(PETSC_COMM_WORLD," Unable to compute small singular value!\n\n");CHKERRQ(ierr);
  } 

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
                    Display solution and clean up
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
  if (nconv1 > 0 && nconv2 > 0) {
    ierr = PetscPrintf(PETSC_COMM_WORLD," Computed singular values: sigma_1=%6f, sigma_n=%6f\n",sigma_1,sigma_n);CHKERRQ(ierr);
    ierr = PetscPrintf(PETSC_COMM_WORLD," Estimated condition number: sigma_1/sigma_n=%6f\n\n",sigma_1/sigma_n);CHKERRQ(ierr);
  }  
 
  /* 
     Free work space
  */
  ierr = SVDDestroy(svd);CHKERRQ(ierr);
  ierr = MatDestroy(A);CHKERRQ(ierr);
  ierr = SlepcFinalize();CHKERRQ(ierr);
  return 0;
}
Example #2
0
int main(int argc,char **argv)
{
  Mat            A;               /* operator matrix */
  Vec            u,v;             /* left and right singular vectors */
  SVD            svd;             /* singular value problem solver context */
  SVDType        type;
  PetscReal      error,tol,sigma,mu=PETSC_SQRT_MACHINE_EPSILON;
  PetscInt       n=100,i,j,Istart,Iend,nsv,maxit,its,nconv;
  PetscErrorCode ierr;

  SlepcInitialize(&argc,&argv,(char*)0,help);

  ierr = PetscOptionsGetInt(NULL,"-n",&n,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsGetReal(NULL,"-mu",&mu,NULL);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD,"\nLauchli singular value decomposition, (%D x %D) mu=%g\n\n",n+1,n,(double)mu);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                          Build the Lauchli matrix
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
  ierr = MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,n+1,n);CHKERRQ(ierr);
  ierr = MatSetFromOptions(A);CHKERRQ(ierr);
  ierr = MatSetUp(A);CHKERRQ(ierr);

  ierr = MatGetOwnershipRange(A,&Istart,&Iend);CHKERRQ(ierr);
  for (i=Istart;i<Iend;i++) {
    if (i == 0) {
      for (j=0;j<n;j++) {
        ierr = MatSetValue(A,0,j,1.0,INSERT_VALUES);CHKERRQ(ierr);
      }
    } else {
      ierr = MatSetValue(A,i,i-1,mu,INSERT_VALUES);CHKERRQ(ierr);
    }
  }

  ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
  ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
  ierr = MatGetVecs(A,&v,&u);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
          Create the singular value solver and set various options
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  /*
     Create singular value solver context
  */
  ierr = SVDCreate(PETSC_COMM_WORLD,&svd);CHKERRQ(ierr);

  /*
     Set operator
  */
  ierr = SVDSetOperator(svd,A);CHKERRQ(ierr);

  /*
     Use thick-restart Lanczos as default solver
  */
  ierr = SVDSetType(svd,SVDTRLANCZOS);CHKERRQ(ierr);

  /*
     Set solver parameters at runtime
  */
  ierr = SVDSetFromOptions(svd);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                      Solve the singular value system
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  ierr = SVDSolve(svd);CHKERRQ(ierr);
  ierr = SVDGetIterationNumber(svd,&its);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD," Number of iterations of the method: %D\n",its);CHKERRQ(ierr);

  /*
     Optional: Get some information from the solver and display it
  */
  ierr = SVDGetType(svd,&type);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD," Solution method: %s\n\n",type);CHKERRQ(ierr);
  ierr = SVDGetDimensions(svd,&nsv,NULL,NULL);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD," Number of requested singular values: %D\n",nsv);CHKERRQ(ierr);
  ierr = SVDGetTolerances(svd,&tol,&maxit);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD," Stopping condition: tol=%.4g, maxit=%D\n",(double)tol,maxit);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                    Display solution and clean up
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  /*
     Get number of converged singular triplets
  */
  ierr = SVDGetConverged(svd,&nconv);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD," Number of converged approximate singular triplets: %D\n\n",nconv);CHKERRQ(ierr);

  if (nconv>0) {
    /*
       Display singular values and relative errors
    */
    ierr = PetscPrintf(PETSC_COMM_WORLD,
         "          sigma           relative error\n"
         "  --------------------- ------------------\n");CHKERRQ(ierr);
    for (i=0;i<nconv;i++) {
      /*
         Get converged singular triplets: i-th singular value is stored in sigma
      */
      ierr = SVDGetSingularTriplet(svd,i,&sigma,u,v);CHKERRQ(ierr);

      /*
         Compute the error associated to each singular triplet
      */
      ierr = SVDComputeRelativeError(svd,i,&error);CHKERRQ(ierr);

      ierr = PetscPrintf(PETSC_COMM_WORLD,"       % 6f      ",(double)sigma);CHKERRQ(ierr);
      ierr = PetscPrintf(PETSC_COMM_WORLD," % 12g\n",(double)error);CHKERRQ(ierr);
    }
    ierr = PetscPrintf(PETSC_COMM_WORLD,"\n");CHKERRQ(ierr);
  }

  /*
     Free work space
  */
  ierr = SVDDestroy(&svd);CHKERRQ(ierr);
  ierr = MatDestroy(&A);CHKERRQ(ierr);
  ierr = VecDestroy(&u);CHKERRQ(ierr);
  ierr = VecDestroy(&v);CHKERRQ(ierr);
  ierr = SlepcFinalize();
  return 0;
}