/*
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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[] = "Diagonal eigenproblem. Illustrates use of shell preconditioner.\n\n"
  "The command line options are:\n"
  "  -n <n>, where <n> = number of grid subdivisions = matrix dimension.\n"
  "  -seed <s>, where <s> = seed for random number generation.\n\n";

#include <slepceps.h>

PetscErrorCode PCApply_User(PC pc,Vec x,Vec y)
{
  PetscErrorCode ierr;

  PetscFunctionBeginUser;
  ierr = VecCopy(x,y);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

int main(int argc,char **argv)
{
  Mat            A;           /* problem matrix */
  EPS            eps;         /* eigenproblem solver context */
  Vec            v0;          /* initial vector */
  PetscRandom    rand;
  PetscReal      tol=PETSC_SMALL;
  PetscInt       n=30,i,Istart,Iend,seed=0x12345678;
  PetscErrorCode ierr;
  ST             st;
  KSP            ksp;
  PC             pc;

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

  ierr = PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);CHKERRQ(ierr);
  ierr = PetscPrintf(PETSC_COMM_WORLD,"\nDiagonal Eigenproblem, n=%D\n\n",n);CHKERRQ(ierr);

  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 = MatSetUp(A);CHKERRQ(ierr);
  ierr = MatGetOwnershipRange(A,&Istart,&Iend);CHKERRQ(ierr);
  for (i=Istart;i<Iend;i++) {
    ierr = MatSetValue(A,i,i,i+1,INSERT_VALUES);CHKERRQ(ierr);
  }
  ierr = MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
  ierr = MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                      Solve the eigensystem
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  ierr = EPSCreate(PETSC_COMM_WORLD,&eps);CHKERRQ(ierr);
  ierr = EPSSetOperators(eps,A,NULL);CHKERRQ(ierr);
  ierr = EPSSetProblemType(eps,EPS_HEP);CHKERRQ(ierr);
  ierr = EPSSetTolerances(eps,tol,PETSC_DEFAULT);CHKERRQ(ierr);
  ierr = EPSSetFromOptions(eps);CHKERRQ(ierr);
  ierr = EPSGetST(eps,&st);CHKERRQ(ierr);
  ierr = STGetKSP(st,&ksp);CHKERRQ(ierr);
  ierr = KSPGetPC(ksp,&pc);CHKERRQ(ierr);
  ierr = PCSetType(pc,PCSHELL);CHKERRQ(ierr);
  ierr = PCShellSetApply(pc,PCApply_User);CHKERRQ(ierr);

  /* set random initial vector */
  ierr = MatCreateVecs(A,&v0,NULL);CHKERRQ(ierr);
  ierr = PetscRandomCreate(PETSC_COMM_WORLD,&rand);CHKERRQ(ierr);
  ierr = PetscRandomSetFromOptions(rand);CHKERRQ(ierr);
  ierr = PetscOptionsGetInt(NULL,NULL,"-seed",&seed,NULL);CHKERRQ(ierr);
  ierr = PetscRandomSetSeed(rand,seed);CHKERRQ(ierr);
  ierr = PetscRandomSeed(rand);CHKERRQ(ierr);
  ierr = VecSetRandom(v0,rand);CHKERRQ(ierr);
  ierr = EPSSetInitialSpace(eps,1,&v0);CHKERRQ(ierr);
  /* call the solver */
  ierr = EPSSolve(eps);CHKERRQ(ierr);

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                    Display solution and clean up
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  ierr = EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL);CHKERRQ(ierr);
  ierr = EPSDestroy(&eps);CHKERRQ(ierr);
  ierr = MatDestroy(&A);CHKERRQ(ierr);
  ierr = VecDestroy(&v0);CHKERRQ(ierr);
  ierr = PetscRandomDestroy(&rand);CHKERRQ(ierr);
  ierr = SlepcFinalize();
  return ierr;
}

/*TEST

   testset:
      requires: !single
      output_file: output/test12_1.out
      test:
         suffix: 1
         args: -eps_type {{krylovschur subspace arnoldi gd jd}} -eps_nev 4
      test:
         suffix: 1_power
         args: -eps_type power -eps_max_it 10000 -eps_nev 4
      test:
         suffix: 1_gd2
         args: -eps_type gd -eps_gd_double_expansion -eps_nev 4

TEST*/
