/*
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   SLEPc - Scalable Library for Eigenvalue Problem Computations
   Copyright (c) 2002-2021, Universitat Politecnica de Valencia, Spain

   This file is part of SLEPc.
   SLEPc is distributed under a 2-clause BSD license (see LICENSE).
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*/

static char help[] = "SVD via the cyclic matrix with a user-provided EPS.\n\n"
  "The command line options are:\n"
  "  -m <m>, where <m> = matrix rows.\n"
  "  -n <n>, where <n> = matrix columns (defaults to m+2).\n\n";

#include <slepcsvd.h>

/*
   This example computes the singular values of a rectangular bidiagonal matrix

              |  1  2                     |
              |     1  2                  |
              |        1  2               |
          A = |          .  .             |
              |             .  .          |
              |                1  2       |
              |                   1  2    |
 */

int main(int argc,char **argv)
{
  Mat                  A;
  SVD                  svd;
  EPS                  eps;
  ST                   st;
  KSP                  ksp;
  PC                   pc;
  PetscInt             m=20,n,Istart,Iend,i,col[2];
  PetscScalar          value[] = { 1, 2 };
  PetscBool            flg,expmat;
  PetscErrorCode       ierr;

  ierr = SlepcInitialize(&argc,&argv,(char*)0,help);if (ierr) return ierr;

  ierr = PetscOptionsGetInt(NULL,NULL,"-m",&m,NULL);CHKERRQ(ierr);
  ierr = PetscOptionsGetInt(NULL,NULL,"-n",&n,&flg);CHKERRQ(ierr);
  if (!flg) n=m+2;
  ierr = PetscPrintf(PETSC_COMM_WORLD,"\nRectangular bidiagonal matrix, m=%D n=%D\n\n",m,n);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        Generate the matrix
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  ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
  ierr = MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,m,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++) {
    col[0]=i; col[1]=i+1;
    if (i<n-1) {
      ierr = MatSetValues(A,1,&i,2,col,value,INSERT_VALUES);CHKERRQ(ierr);
    } else if (i==n-1) {
      ierr = MatSetValue(A,i,col[0],value[0],INSERT_VALUES);CHKERRQ(ierr);
    }
  }
  ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
  ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        Create a standalone EPS with appropriate settings
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  ierr = EPSCreate(PETSC_COMM_WORLD,&eps);CHKERRQ(ierr);
  ierr = EPSSetWhichEigenpairs(eps,EPS_TARGET_MAGNITUDE);CHKERRQ(ierr);
  ierr = EPSSetTarget(eps,1.0);CHKERRQ(ierr);
  ierr = EPSGetST(eps,&st);CHKERRQ(ierr);
  ierr = STSetType(st,STSINVERT);CHKERRQ(ierr);
  ierr = STSetShift(st,1.01);CHKERRQ(ierr);
  ierr = STGetKSP(st,&ksp);CHKERRQ(ierr);
  ierr = KSPSetType(ksp,KSPPREONLY);CHKERRQ(ierr);
  ierr = KSPGetPC(ksp,&pc);CHKERRQ(ierr);
  ierr = PCSetType(pc,PCLU);CHKERRQ(ierr);
  ierr = EPSSetFromOptions(eps);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
        Compute singular values
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  ierr = SVDCreate(PETSC_COMM_WORLD,&svd);CHKERRQ(ierr);
  ierr = SVDSetOperators(svd,A,NULL);CHKERRQ(ierr);
  ierr = SVDSetType(svd,SVDCYCLIC);CHKERRQ(ierr);
  ierr = SVDCyclicSetEPS(svd,eps);CHKERRQ(ierr);
  ierr = SVDCyclicSetExplicitMatrix(svd,PETSC_TRUE);CHKERRQ(ierr);
  ierr = SVDSetWhichSingularTriplets(svd,SVD_SMALLEST);CHKERRQ(ierr);
  ierr = SVDSetFromOptions(svd);CHKERRQ(ierr);
  ierr = PetscObjectTypeCompare((PetscObject)svd,SVDCYCLIC,&flg);CHKERRQ(ierr);
  if (flg) {
    ierr = SVDCyclicGetExplicitMatrix(svd,&expmat);CHKERRQ(ierr);
    if (expmat) {
      ierr = PetscPrintf(PETSC_COMM_WORLD," Using explicit matrix with cyclic solver\n");CHKERRQ(ierr);
    }
  }
  ierr = SVDSolve(svd);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                    Display solution and clean up
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  ierr = SVDErrorView(svd,SVD_ERROR_RELATIVE,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
  ierr = SVDDestroy(&svd);CHKERRQ(ierr);
  ierr = EPSDestroy(&eps);CHKERRQ(ierr);
  ierr = MatDestroy(&A);CHKERRQ(ierr);
  ierr = SlepcFinalize();
  return ierr;
}

/*TEST

   test:
      suffix: 1
      args: -log_exclude svd

   test:
      suffix: 2_cuda
      args: -log_exclude svd -mat_type aijcusparse
      requires: cuda
      output_file: output/test7_1.out

TEST*/
