Date: 2024-04-26T10:22:05+00:00

Actual source code: ex12.c
slepc-3.21.1 2024-04-26
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      1: /*
      2:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      3:    SLEPc - Scalable Library for Eigenvalue Problem Computations
      4:    Copyright (c) 2002-, Universitat Politecnica de Valencia, Spain

      6:    This file is part of SLEPc.
      7:    SLEPc is distributed under a 2-clause BSD license (see LICENSE).
      8:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      9: */

     11: static char help[] = "Compute all eigenvalues in an interval of a symmetric-definite problem.\n\n"
     12:   "The command line options are:\n"
     13:   "  -n <n>, where <n> = number of grid subdivisions in x dimension.\n"
     14:   "  -m <m>, where <m> = number of grid subdivisions in y dimension.\n\n";

     16: #include <slepceps.h>

     18: int main(int argc,char **argv)
     19: {
     20:   Mat            A,B;         /* matrices */
     21:   EPS            eps;         /* eigenproblem solver context */
     22:   ST             st;          /* spectral transformation context */
     23:   KSP            ksp;
     24:   PC             pc;
     25:   PetscInt       N,n=35,m,Istart,Iend,II,nev,i,j,k,*inertias;
     26:   PetscBool      flag,showinertia=PETSC_TRUE;
     27:   PetscReal      int0,int1,*shifts;

     29:   PetscFunctionBeginUser;
     30:   PetscCall(SlepcInitialize(&argc,&argv,(char*)0,help));

     32:   PetscCall(PetscOptionsGetBool(NULL,NULL,"-showinertia",&showinertia,NULL));
     33:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL));
     34:   PetscCall(PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag));
     35:   if (!flag) m=n;
     36:   N = n*m;
     37:   PetscCall(PetscPrintf(PETSC_COMM_WORLD,"\nSymmetric-definite problem with two intervals, N=%" PetscInt_FMT " (%" PetscInt_FMT "x%" PetscInt_FMT " grid)\n\n",N,n,m));

     39:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     40:      Compute the matrices that define the eigensystem, Ax=kBx
     41:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     43:   PetscCall(MatCreate(PETSC_COMM_WORLD,&A));
     44:   PetscCall(MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N));
     45:   PetscCall(MatSetFromOptions(A));

     47:   PetscCall(MatCreate(PETSC_COMM_WORLD,&B));
     48:   PetscCall(MatSetSizes(B,PETSC_DECIDE,PETSC_DECIDE,N,N));
     49:   PetscCall(MatSetFromOptions(B));

     51:   PetscCall(MatGetOwnershipRange(A,&Istart,&Iend));
     52:   for (II=Istart;II<Iend;II++) {
     53:     i = II/n; j = II-i*n;
     54:     if (i>0) PetscCall(MatSetValue(A,II,II-n,-1.0,INSERT_VALUES));
     55:     if (i<m-1) PetscCall(MatSetValue(A,II,II+n,-1.0,INSERT_VALUES));
     56:     if (j>0) PetscCall(MatSetValue(A,II,II-1,-1.0,INSERT_VALUES));
     57:     if (j<n-1) PetscCall(MatSetValue(A,II,II+1,-1.0,INSERT_VALUES));
     58:     PetscCall(MatSetValue(A,II,II,4.0,INSERT_VALUES));
     59:     PetscCall(MatSetValue(B,II,II,2.0,INSERT_VALUES));
     60:   }
     61:   if (Istart==0) {
     62:     PetscCall(MatSetValue(B,0,0,6.0,INSERT_VALUES));
     63:     PetscCall(MatSetValue(B,0,1,-1.0,INSERT_VALUES));
     64:     PetscCall(MatSetValue(B,1,0,-1.0,INSERT_VALUES));
     65:     PetscCall(MatSetValue(B,1,1,1.0,INSERT_VALUES));
     66:   }

     68:   PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
     69:   PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));
     70:   PetscCall(MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY));
     71:   PetscCall(MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY));

     73:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     74:                 Create the eigensolver and set various options
     75:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     77:   PetscCall(EPSCreate(PETSC_COMM_WORLD,&eps));
     78:   PetscCall(EPSSetOperators(eps,A,B));
     79:   PetscCall(EPSSetProblemType(eps,EPS_GHEP));

     81:   /*
     82:      Set first interval and other settings for spectrum slicing
     83:   */
     84:   PetscCall(EPSSetType(eps,EPSKRYLOVSCHUR));
     85:   PetscCall(EPSSetWhichEigenpairs(eps,EPS_ALL));
     86:   PetscCall(EPSSetInterval(eps,1.1,1.3));
     87:   PetscCall(EPSGetST(eps,&st));
     88:   PetscCall(STSetType(st,STSINVERT));
     89:   PetscCall(EPSKrylovSchurGetKSP(eps,&ksp));
     90:   PetscCall(KSPGetPC(ksp,&pc));
     91:   PetscCall(KSPSetType(ksp,KSPPREONLY));
     92:   PetscCall(PCSetType(pc,PCCHOLESKY));
     93:   PetscCall(EPSSetFromOptions(eps));

     95:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     96:                  Solve for first interval and display info
     97:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     99:   PetscCall(EPSSolve(eps));
    100:   PetscCall(EPSGetDimensions(eps,&nev,NULL,NULL));
    101:   PetscCall(EPSGetInterval(eps,&int0,&int1));
    102:   PetscCall(PetscPrintf(PETSC_COMM_WORLD," Found %" PetscInt_FMT " eigenvalues in interval [%g,%g]\n",nev,(double)int0,(double)int1));
    103:   if (showinertia) {
    104:     PetscCall(EPSKrylovSchurGetInertias(eps,&k,&shifts,&inertias));
    105:     PetscCall(PetscPrintf(PETSC_COMM_WORLD," Used %" PetscInt_FMT " shifts (inertia):\n",k));
    106:     for (i=0;i<k;i++) PetscCall(PetscPrintf(PETSC_COMM_WORLD," .. %g (%" PetscInt_FMT ")\n",(double)shifts[i],inertias[i]));
    107:     PetscCall(PetscFree(shifts));
    108:     PetscCall(PetscFree(inertias));
    109:   }

    111:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    112:                  Solve for second interval and display info
    113:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
    114:   PetscCall(EPSSetInterval(eps,1.499,1.6));
    115:   PetscCall(EPSSolve(eps));
    116:   PetscCall(EPSGetDimensions(eps,&nev,NULL,NULL));
    117:   PetscCall(EPSGetInterval(eps,&int0,&int1));
    118:   PetscCall(PetscPrintf(PETSC_COMM_WORLD," Found %" PetscInt_FMT " eigenvalues in interval [%g,%g]\n",nev,(double)int0,(double)int1));
    119:   if (showinertia) {
    120:     PetscCall(EPSKrylovSchurGetInertias(eps,&k,&shifts,&inertias));
    121:     PetscCall(PetscPrintf(PETSC_COMM_WORLD," Used %" PetscInt_FMT " shifts (inertia):\n",k));
    122:     for (i=0;i<k;i++) PetscCall(PetscPrintf(PETSC_COMM_WORLD," .. %g (%" PetscInt_FMT ")\n",(double)shifts[i],inertias[i]));
    123:     PetscCall(PetscFree(shifts));
    124:     PetscCall(PetscFree(inertias));
    125:   }

    127:   PetscCall(EPSDestroy(&eps));
    128:   PetscCall(MatDestroy(&A));
    129:   PetscCall(MatDestroy(&B));
    130:   PetscCall(SlepcFinalize());
    131:   return 0;
    132: }

    134: /*TEST

    136:    test:
    137:       suffix: 1
    138:       args: -showinertia 0 -eps_error_relative
    139:       requires: !single

    141: TEST*/