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:   PetscErrorCode (*checkh)(void *, Vec, Vec, PetscScalar *);
 40:   void *checkhctx; /* optional context used by MatMFFDSetCheckh() */

 42:   PetscErrorCode (*func)(void *, Vec, Vec); /* 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:   PetscErrorCode (*funci)(void *, PetscInt, Vec, PetscScalar *); /* Evaluates func_[i]() */
 49:   PetscErrorCode (*funcisetbase)(void *, Vec);                   /* 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 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);