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: #include <slepc/private/slepcimpl.h>

 13: /*@
 14:    MatCreateBSE - Create a matrix that can be used to define a structured eigenvalue
 15:    problem of type BSE (Bethe-Salpeter Equation).

 17:    Collective

 19:    Input Parameters:
 20: +  R - matrix for the diagonal block (resonant)
 21: -  C - matrix for the off-diagonal block (coupling)

 23:    Output Parameter:
 24: .  H  - the resulting matrix

 26:    Notes:
 27:    The resulting matrix has the block form H = [ R C; -C^H -R^T ], where R is assumed
 28:    to be (complex) Hermitian and C complex symmetric. Note that this function does
 29:    not check these properties, so if the matrices provided by the user do not satisfy
 30:    them, then the solver will not behave as expected.

 32:    The obtained matrix can be used as an input matrix to EPS eigensolvers via
 33:    EPSSetOperators() for the case that the problem type is EPS_BSE. Note that the user
 34:    cannot just build a matrix with the required structure, it must be done via this
 35:    function.

 37:    In the current implementation, H is a MATNEST matrix, where R and C form the top
 38:    block row, while the bottom block row is composed of matrices of type
 39:    MATTRANSPOSEVIRTUAL and MATHERMITIANTRANSPOSEVIRTUAL scaled by -1.

 41:    Level: intermediate

 43: .seealso: MatCreateNest(), EPSSetOperators(), EPSSetProblemType()
 44: @*/
 45: PetscErrorCode MatCreateBSE(Mat R,Mat C,Mat *H)
 46: {
 47:   PetscInt       Mr,Mc,Nr,Nc,mr,mc,nr,nc;
 48:   Mat            block[4] = { R, C, NULL, NULL };
 49:   SlepcMatStruct mctx;

 51:   PetscFunctionBegin;
 54:   PetscCheckSameTypeAndComm(R,1,C,2);
 55:   PetscAssertPointer(H,3);

 57:   /* check sizes */
 58:   PetscCall(MatGetSize(R,&Mr,&Nr));
 59:   PetscCall(MatGetLocalSize(R,&mr,&nr));
 60:   PetscCall(MatGetSize(C,&Mc,&Nc));
 61:   PetscCall(MatGetLocalSize(C,&mc,&nc));
 62:   PetscCheck(Mc==Mr && mc==mr,PetscObjectComm((PetscObject)R),PETSC_ERR_ARG_INCOMP,"Incompatible row dimensions");
 63:   PetscCheck(Nc==Nr && nc==nr,PetscObjectComm((PetscObject)R),PETSC_ERR_ARG_INCOMP,"Incompatible column dimensions");

 65:   /* bottom block row */
 66:   PetscCall(MatCreateHermitianTranspose(C,&block[2]));
 67:   PetscCall(MatScale(block[2],-1.0));
 68:   PetscCall(MatCreateTranspose(R,&block[3]));
 69:   PetscCall(MatScale(block[3],-1.0));

 71:   /* create nest matrix and compose context */
 72:   PetscCall(MatCreateNest(PetscObjectComm((PetscObject)R),2,NULL,2,NULL,block,H));
 73:   PetscCall(MatDestroy(&block[2]));
 74:   PetscCall(MatDestroy(&block[3]));

 76:   PetscCall(PetscNew(&mctx));
 77:   mctx->cookie = SLEPC_MAT_STRUCT_BSE;
 78:   PetscCall(PetscObjectContainerCompose((PetscObject)*H,"SlepcMatStruct",mctx,PetscCtxDestroyDefault));
 79:   PetscFunctionReturn(PETSC_SUCCESS);
 80: }