1: /*
  2:     This file should be included in NEW routines that compute the
  3:     differencing parameter for finite difference based matrix-free
  4:     methods.  For example, such routines can compute h for use in
  5:     Jacobian-vector products of the form

  7:                        F(x+ha) - F(x)
  8:           F'(u)a  ~=  ----------------
  9:                             h
 10: */
 11: #pragma once

 13: #include <petscmat.h>
 14: #include <petsc/private/petscimpl.h>

 16: /*
 17:  Table of functions that manage the computation and understanding
 18:  of the parameter for finite difference based matrix-free computations
 19: */
 20: struct _MFOps {
 21:   PetscErrorCode (*compute)(MatMFFD, Vec, Vec, PetscScalar *, PetscBool *zeroa);
 22:   PetscErrorCode (*view)(MatMFFD, PetscViewer);
 23:   PetscErrorCode (*destroy)(MatMFFD);
 24:   PetscErrorCode (*setfromoptions)(MatMFFD, PetscOptionItems);
 25: };

 27: /* context for default matrix-free SNES */
 28: struct _p_MatMFFD {
 29:   PETSCHEADER(struct _MFOps);
 30:   Vec              w;         /* work vector */
 31:   PetscReal        error_rel; /* square root of relative error in computing function */
 32:   PetscScalar      currenth;  /* last differencing parameter h used */
 33:   PetscScalar     *historyh;  /* history of differencing parameter h */
 34:   PetscInt         ncurrenth, maxcurrenth;
 35:   void            *hctx;
 36:   Mat              mat;             /* back reference to shell matrix that contains this */
 37:   PetscInt         recomputeperiod; /* how often the h is recomputed; default to 1 */
 38:   PetscInt         count;           /* used by recomputeperiod */
 39:   MatMFFDCheckhFn *checkh;
 40:   void            *checkhctx; /* optional context used by MatMFFDSetCheckh() */

 42:   MatMFFDFn *func;      /* function used for matrix-free */
 43:   void      *funcctx;   /* the context for the function */
 44:   Vec        current_f; /* location of F(u); used with F(u+h) */
 45:   PetscBool  current_f_allocated;
 46:   Vec        current_u; /* location of u; used with F(u+h) */

 48:   MatMFFDiFn     *funci;        /* Evaluates func_[i]() */
 49:   MatMFFDiBaseFn *funcisetbase; /* Sets base for future evaluations of func_[i]() */

 51:   void *ctx; /* this is used by MatCreateSNESMF() to store the SNES object */
 52: #if defined(PETSC_USE_COMPLEX)
 53:   PetscBool usecomplex; /* use the Lyness complex number trick to compute the matrix-vector product */
 54: #endif
 55: };

 57: PETSC_EXTERN PetscFunctionList MatMFFDList;
 58: PETSC_EXTERN PetscBool         MatMFFDRegisterAllCalled;
 59: PETSC_EXTERN PetscErrorCode    MatMFFDRegisterAll(void);