/*
   - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   SLEPc - Scalable Library for Eigenvalue Problem Computations
   Copyright (c) 2002-, 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[] = "Solve a quadratic problem with PEPLINEAR with a user-provided EPS.\n\n"
  "The command line options are:\n"
  "  -n <n>, where <n> = number of grid subdivisions in x dimension.\n"
  "  -m <m>, where <m> = number of grid subdivisions in y dimension.\n\n";

#include <slepcpep.h>

int main(int argc,char **argv)
{
  Mat            M,C,K,A[3];
  PEP            pep;
  PetscInt       N,n=10,m,Istart,Iend,II,i,j;
  PetscBool      flag,expmat;
  PetscReal      alpha,beta;
  EPS            eps;
  ST             st;
  KSP            ksp;
  PC             pc;

  PetscCall(SlepcInitialize(&argc,&argv,(char*)0,help));
  PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL));
  PetscCall(PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag));
  if (!flag) m=n;
  N = n*m;
  PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\nQuadratic Eigenproblem, N=%" PetscInt_FMT " (%" PetscInt_FMT "x%" PetscInt_FMT " grid)\n\n",N,n,m));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     Compute the matrices that define the eigensystem, (k^2*M+k*C+K)x=0
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  /* K is the 2-D Laplacian */
  PetscCall(MatCreate(PETSC_COMM_WORLD,&K));
  PetscCall(MatSetSizes(K,PETSC_DECIDE,PETSC_DECIDE,N,N));
  PetscCall(MatSetFromOptions(K));
  PetscCall(MatSetUp(K));
  PetscCall(MatGetOwnershipRange(K,&Istart,&Iend));
  for (II=Istart;II<Iend;II++) {
    i = II/n; j = II-i*n;
    if (i>0) PetscCall(MatSetValue(K,II,II-n,-1.0,INSERT_VALUES));
    if (i<m-1) PetscCall(MatSetValue(K,II,II+n,-1.0,INSERT_VALUES));
    if (j>0) PetscCall(MatSetValue(K,II,II-1,-1.0,INSERT_VALUES));
    if (j<n-1) PetscCall(MatSetValue(K,II,II+1,-1.0,INSERT_VALUES));
    PetscCall(MatSetValue(K,II,II,4.0,INSERT_VALUES));
  }
  PetscCall(MatAssemblyBegin(K,MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(K,MAT_FINAL_ASSEMBLY));

  /* C is the 1-D Laplacian on horizontal lines */
  PetscCall(MatCreate(PETSC_COMM_WORLD,&C));
  PetscCall(MatSetSizes(C,PETSC_DECIDE,PETSC_DECIDE,N,N));
  PetscCall(MatSetFromOptions(C));
  PetscCall(MatSetUp(C));
  PetscCall(MatGetOwnershipRange(C,&Istart,&Iend));
  for (II=Istart;II<Iend;II++) {
    i = II/n; j = II-i*n;
    if (j>0) PetscCall(MatSetValue(C,II,II-1,-1.0,INSERT_VALUES));
    if (j<n-1) PetscCall(MatSetValue(C,II,II+1,-1.0,INSERT_VALUES));
    PetscCall(MatSetValue(C,II,II,2.0,INSERT_VALUES));
  }
  PetscCall(MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY));

  /* M is a diagonal matrix */
  PetscCall(MatCreate(PETSC_COMM_WORLD,&M));
  PetscCall(MatSetSizes(M,PETSC_DECIDE,PETSC_DECIDE,N,N));
  PetscCall(MatSetFromOptions(M));
  PetscCall(MatSetUp(M));
  PetscCall(MatGetOwnershipRange(M,&Istart,&Iend));
  for (II=Istart;II<Iend;II++) PetscCall(MatSetValue(M,II,II,(PetscReal)(II+1),INSERT_VALUES));
  PetscCall(MatAssemblyBegin(M,MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(M,MAT_FINAL_ASSEMBLY));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
             Create a standalone EPS with appropriate settings
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  PetscCall(EPSCreate(PETSC_COMM_WORLD,&eps));
  PetscCall(EPSSetWhichEigenpairs(eps,EPS_TARGET_MAGNITUDE));
#if defined(PETSC_USE_COMPLEX)
  PetscCall(EPSSetTarget(eps,0.01*PETSC_i));
#endif
  PetscCall(EPSGetST(eps,&st));
  PetscCall(STSetType(st,STSINVERT));
  PetscCall(STGetKSP(st,&ksp));
  PetscCall(KSPSetType(ksp,KSPBCGS));
  PetscCall(KSPGetPC(ksp,&pc));
  PetscCall(PCSetType(pc,PCJACOBI));
  PetscCall(EPSSetFromOptions(eps));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
             Create the eigensolver and solve the eigensystem
     - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

  PetscCall(PEPCreate(PETSC_COMM_WORLD,&pep));
  PetscCall(PetscObjectSetName((PetscObject)pep,"PEP_solver"));
  A[0] = K; A[1] = C; A[2] = M;
  PetscCall(PEPSetOperators(pep,3,A));
  PetscCall(PEPSetType(pep,PEPLINEAR));
  PetscCall(PEPSetProblemType(pep,PEP_GENERAL));
  PetscCall(PEPLinearSetEPS(pep,eps));
  PetscCall(PEPSetFromOptions(pep));
  PetscCall(PEPSolve(pep));
  PetscCall(PEPLinearGetLinearization(pep,&alpha,&beta));
  PetscCall(PetscPrintf(PETSC_COMM_WORLD," Linearization with alpha=%g, beta=%g",(double)alpha,(double)beta));
  PetscCall(PEPLinearGetExplicitMatrix(pep,&expmat));
  if (expmat) PetscCall(PetscPrintf(PETSC_COMM_WORLD," with explicit matrix"));
  PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\n"));

  /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                    Display solution and clean up
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  PetscCall(PEPErrorView(pep,PEP_ERROR_BACKWARD,NULL));
  PetscCall(PEPDestroy(&pep));
  PetscCall(EPSDestroy(&eps));
  PetscCall(MatDestroy(&M));
  PetscCall(MatDestroy(&C));
  PetscCall(MatDestroy(&K));
  PetscCall(SlepcFinalize());
  return 0;
}

/*TEST

   testset:
      args: -pep_linear_explicitmatrix -pep_view_vectors ::ascii_info
      test:
         suffix: 1_real
         requires: !single !complex
      test:
         suffix: 1
         requires: !single complex

TEST*/
