1: /*
  2:    Context for a Newton trust region method for solving a system
  3:    of nonlinear equations
  4:  */

  6: #pragma once
  7: #include <petsc/private/snesimpl.h>

  9: typedef struct {
 10:   PetscReal delta; /* trust region radius */

 12:   PetscObjectParameterDeclare(PetscReal, delta0); /* initial radius for trust region */
 13:   PetscObjectParameterDeclare(PetscReal, deltaM); /* maximum radius for trust region */
 14:   PetscObjectParameterDeclare(PetscReal, deltam); /* minimum radius for trust region */

 16:   PetscReal kmdc; /* sufficient decrease parameter */

 18:   /*
 19:     Given rho = (fk - fkp1) / (m(0) - m(pk))

 21:     The radius is modified as:
 22:       rho < eta2 -> delta *= t1
 23:       rho > eta3 -> delta *= t2
 24:       delta = min(delta,deltaM)

 26:     The step is accepted if rho > eta1
 27:     The iterative process is halted if delta < deltam
 28:   */
 29:   PetscObjectParameterDeclare(PetscReal, eta1);
 30:   PetscObjectParameterDeclare(PetscReal, eta2);
 31:   PetscObjectParameterDeclare(PetscReal, eta3);
 32:   PetscObjectParameterDeclare(PetscReal, t1);
 33:   PetscObjectParameterDeclare(PetscReal, t2);

 35:   /* Use quasi-Newton models for J and (possibly different) Jp */
 36:   SNESNewtonTRQNType qn;
 37:   Mat                qnB;
 38:   Mat                qnB_pre;

 40:   /* The type of norm for the trust region */
 41:   NormType norm;

 43:   SNESNewtonTRFallbackType fallback; /* enum to distinguish fallback in case Newton step is outside of the trust region */

 45:   PetscErrorCode (*precheck)(SNES, Vec, Vec, PetscBool *, void *);
 46:   void *precheckctx;
 47:   PetscErrorCode (*postcheck)(SNES, Vec, Vec, Vec, PetscBool *, PetscBool *, void *);
 48:   void *postcheckctx;
 49: } SNES_NEWTONTR;