/*
   Context for using preconditioned conjugate gradient method to minimized a
   quadratic function subject to a trust region constraint.  If the matrix
   is indefinite, a direction of negative curvature may be encountered.  If
   a direction of negative curvature is found, we continue to build the
   tridiagonal Lanczos matrix for a fixed number of iterations.  After this
   matrix is computed, we compute a global solution to solve the trust-
   region problem with the tridiagonal approximation by using a variant of
   the More'-Sorenson algorithm.  The direction is then constructed from
   this solution.

   This method is described in:
     N. Gould, S. Lucidi, M. Roma, and Ph. Toint, "Solving the Trust-Region
       Subproblem using the Lanczos Method", SIAM Journal on Optimization,
       9, pages 504-525, 1999.
*/

#pragma once

#include <petsc/private/kspimpl.h>

typedef struct {
  PetscReal *diag;   /* Diagonal part of Lanczos matrix           */
  PetscReal *offd;   /* Off-diagonal part of Lanczos matrix       */
  PetscReal *alpha;  /* Record of alpha values from CG            */
  PetscReal *beta;   /* Record of beta values from CG             */
  PetscReal *norm_r; /* Record of residual values from CG         */

  PetscReal    *rwork; /* Real workspace for solver computations    */
  PetscBLASInt *iwork; /* Integer workspace for solver computations */

  PetscReal radius;
  PetscReal norm_d;
  PetscReal e_min;
  PetscReal o_fcn;
  PetscReal lambda;

  PetscReal init_pert;  /* Initial perturbation for solve            */
  PetscReal eigen_tol;  /* Tolerance used when computing eigenvalue  */
  PetscReal newton_tol; /* Tolerance used for newton method          */

  PetscInt alloced;    /* Size of workspace vectors allocated       */
  PetscInt init_alloc; /* Initial size for workspace vectors        */

  PetscInt max_lanczos_its; /* Maximum lanczos iterations                */
  PetscInt max_newton_its;  /* Maximum newton iterations                 */
  PetscInt dtype;           /* Method used to measure the norm of step   */
} KSPCG_GLTR;
