Date: 2022-08-09T09:05:42+00:00

Actual source code: ex47.c
slepc-3.17.2 2022-08-09
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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[] = "Shows how to recover symmetry when solving a GHEP as non-symmetric.\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: /*
     19:    User context for shell matrix
     20: */
     21: typedef struct {
     22:   KSP       ksp;
     23:   Mat       B;
     24:   Vec       w;
     25: } CTX_SHELL;

     27: /*
     28:     Matrix-vector product function for user matrix
     29:        y <-- A^{-1}*B*x
     30:     The matrix A^{-1}*B*x is not symmetric, but it is self-adjoint with respect
     31:     to the B-inner product. Here we assume A is symmetric and B is SPD.
     32:  */
     33: PetscErrorCode MatMult_Sinvert0(Mat S,Vec x,Vec y)
     34: {
     35:   CTX_SHELL      *ctx;

     38:   MatShellGetContext(S,&ctx);
     39:   MatMult(ctx->B,x,ctx->w);
     40:   KSPSolve(ctx->ksp,ctx->w,y);
     41:   PetscFunctionReturn(0);
     42: }

     44: int main(int argc,char **argv)
     45: {
     46:   Mat               A,B,S;      /* matrices */
     47:   EPS               eps;        /* eigenproblem solver context */
     48:   BV                bv;
     49:   Vec               *X,v;
     50:   PetscReal         lev=0.0,tol=1000*PETSC_MACHINE_EPSILON;
     51:   PetscInt          N,n=45,m,Istart,Iend,II,i,j,nconv;
     52:   PetscBool         flag;
     53:   CTX_SHELL         *ctx;

     55:   SlepcInitialize(&argc,&argv,(char*)0,help);
     56:   PetscOptionsGetInt(NULL,NULL,"-n",&n,NULL);
     57:   PetscOptionsGetInt(NULL,NULL,"-m",&m,&flag);
     58:   if (!flag) m=n;
     59:   N = n*m;
     60:   PetscPrintf(PETSC_COMM_WORLD,"\nGeneralized Symmetric Eigenproblem, N=%" PetscInt_FMT " (%" PetscInt_FMT "x%" PetscInt_FMT " grid)\n\n",N,n,m);

     62:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     63:          Compute the matrices that define the eigensystem, Ax=kBx
     64:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

     66:   MatCreate(PETSC_COMM_WORLD,&A);
     67:   MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N);
     68:   MatSetFromOptions(A);
     69:   MatSetUp(A);

     71:   MatCreate(PETSC_COMM_WORLD,&B);
     72:   MatSetSizes(B,PETSC_DECIDE,PETSC_DECIDE,N,N);
     73:   MatSetFromOptions(B);
     74:   MatSetUp(B);

     76:   MatGetOwnershipRange(A,&Istart,&Iend);
     77:   for (II=Istart;II<Iend;II++) {
     78:     i = II/n; j = II-i*n;
     79:     if (i>0) MatSetValue(A,II,II-n,-1.0,INSERT_VALUES);
     80:     if (i<m-1) MatSetValue(A,II,II+n,-1.0,INSERT_VALUES);
     81:     if (j>0) MatSetValue(A,II,II-1,-1.0,INSERT_VALUES);
     82:     if (j<n-1) MatSetValue(A,II,II+1,-1.0,INSERT_VALUES);
     83:     MatSetValue(A,II,II,4.0,INSERT_VALUES);
     84:     MatSetValue(B,II,II,2.0/PetscLogScalar(II+2),INSERT_VALUES);
     85:   }

     87:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
     88:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);
     89:   MatAssemblyBegin(B,MAT_FINAL_ASSEMBLY);
     90:   MatAssemblyEnd(B,MAT_FINAL_ASSEMBLY);
     91:   MatCreateVecs(B,&v,NULL);

     93:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
     94:               Create a shell matrix S = A^{-1}*B
     95:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
     96:   PetscNew(&ctx);
     97:   KSPCreate(PETSC_COMM_WORLD,&ctx->ksp);
     98:   KSPSetOperators(ctx->ksp,A,A);
     99:   KSPSetTolerances(ctx->ksp,tol,PETSC_DEFAULT,PETSC_DEFAULT,PETSC_DEFAULT);
    100:   KSPSetFromOptions(ctx->ksp);
    101:   ctx->B = B;
    102:   MatCreateVecs(A,&ctx->w,NULL);
    103:   MatCreateShell(PETSC_COMM_WORLD,PETSC_DECIDE,PETSC_DECIDE,N,N,(void*)ctx,&S);
    104:   MatShellSetOperation(S,MATOP_MULT,(void(*)(void))MatMult_Sinvert0);

    106:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    107:                 Create the eigensolver and set various options
    108:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    110:   EPSCreate(PETSC_COMM_WORLD,&eps);
    111:   EPSSetOperators(eps,S,NULL);
    112:   EPSSetProblemType(eps,EPS_HEP);  /* even though S is not symmetric */
    113:   EPSSetTolerances(eps,tol,PETSC_DEFAULT);
    114:   EPSSetFromOptions(eps);

    116:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    117:                       Solve the eigensystem
    118:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    120:   EPSSetUp(eps);   /* explicitly call setup */
    121:   EPSGetBV(eps,&bv);
    122:   BVSetMatrix(bv,B,PETSC_FALSE);  /* set inner product matrix to recover symmetry */
    123:   EPSSolve(eps);

    125:   /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    126:                  Display solution and check B-orthogonality
    127:      - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

    129:   EPSGetTolerances(eps,&tol,NULL);
    130:   EPSErrorView(eps,EPS_ERROR_RELATIVE,NULL);
    131:   EPSGetConverged(eps,&nconv);
    132:   if (nconv>1) {
    133:     VecDuplicateVecs(v,nconv,&X);
    134:     for (i=0;i<nconv;i++) EPSGetEigenvector(eps,i,X[i],NULL);
    135:     VecCheckOrthonormality(X,nconv,NULL,nconv,B,NULL,&lev);
    136:     if (lev<10*tol) PetscPrintf(PETSC_COMM_WORLD,"Level of orthogonality below the tolerance\n");
    137:     else PetscPrintf(PETSC_COMM_WORLD,"Level of orthogonality: %g\n",(double)lev);
    138:     VecDestroyVecs(nconv,&X);
    139:   }

    141:   EPSDestroy(&eps);
    142:   MatDestroy(&A);
    143:   MatDestroy(&B);
    144:   VecDestroy(&v);
    145:   KSPDestroy(&ctx->ksp);
    146:   VecDestroy(&ctx->w);
    147:   PetscFree(ctx);
    148:   MatDestroy(&S);
    149:   SlepcFinalize();
    150:   return 0;
    151: }

    153: /*TEST

    155:    test:
    156:       args: -n 18 -eps_nev 4 -eps_max_it 1500
    157:       requires: !single

    159: TEST*/