/* multimin/conjugate_pr.c
 * 
 * Copyright (C) 1996, 1997, 1998, 1999, 2000 Fabrice Rossi
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or (at
 * your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

/* conjugate_pr.c -- Conjugate gradient Polak-Ribiere algorithm */

/* Modified by Brian Gough to use single iteration structure */

#include <config.h>
#include <gsl/gsl_multimin.h>
#include <gsl/gsl_blas.h>

#include "directional_minimize.c"

typedef struct
{
  int iter;
  double step;
  double max_step;
  double tol;
  gsl_vector *x1;
  gsl_vector *dx1;
  gsl_vector *x2;
  double pnorm;
  gsl_vector *p;
  double g0norm;
  gsl_vector *g0;
}
conjugate_pr_state_t;

static int
conjugate_pr_alloc (void *vstate, size_t n)
{
  conjugate_pr_state_t *state = (conjugate_pr_state_t *) vstate;

  state->x1 = gsl_vector_calloc (n);

  if (state->x1 == 0)
    {
      GSL_ERROR ("failed to allocate space for x1", GSL_ENOMEM);
    }

  state->dx1 = gsl_vector_calloc (n);

  if (state->dx1 == 0)
    {
      gsl_vector_free (state->x1);
      GSL_ERROR ("failed to allocate space for dx1", GSL_ENOMEM);
    }

  state->x2 = gsl_vector_calloc (n);

  if (state->x2 == 0)
    {
      gsl_vector_free (state->dx1);
      gsl_vector_free (state->x1);
      GSL_ERROR ("failed to allocate space for x2", GSL_ENOMEM);
    }

  state->p = gsl_vector_calloc (n);

  if (state->p == 0)
    {
      gsl_vector_free (state->x2);
      gsl_vector_free (state->dx1);
      gsl_vector_free (state->x1);
      GSL_ERROR ("failed to allocate space for p", GSL_ENOMEM);
    }

  state->g0 = gsl_vector_calloc (n);

  if (state->g0 == 0)
    {
      gsl_vector_free (state->p);
      gsl_vector_free (state->x2);
      gsl_vector_free (state->dx1);
      gsl_vector_free (state->x1);
      GSL_ERROR ("failed to allocate space for g0", GSL_ENOMEM);
    }

  return GSL_SUCCESS;
}

static int
conjugate_pr_set (void *vstate, gsl_multimin_function_fdf * fdf,
                  const gsl_vector * x, double *f, gsl_vector * gradient,
                  double step_size, double tol)
{
  conjugate_pr_state_t *state = (conjugate_pr_state_t *) vstate;

  state->iter = 0;
  state->step = step_size;
  state->max_step = step_size;
  state->tol = tol;

  GSL_MULTIMIN_FN_EVAL_F_DF (fdf, x, f, gradient);

  /* Use the gradient as the initial direction */

  gsl_vector_memcpy (state->p, gradient);
  gsl_vector_memcpy (state->g0, gradient);

  {
    double gnorm = gsl_blas_dnrm2 (gradient);

    state->pnorm = gnorm;
    state->g0norm = gnorm;
  }

  return GSL_SUCCESS;
}

static void
conjugate_pr_free (void *vstate)
{
  conjugate_pr_state_t *state = (conjugate_pr_state_t *) vstate;

  gsl_vector_free (state->g0);
  gsl_vector_free (state->p);
  gsl_vector_free (state->x2);
  gsl_vector_free (state->dx1);
  gsl_vector_free (state->x1);
}

static int
conjugate_pr_restart (void *vstate)
{
  conjugate_pr_state_t *state = (conjugate_pr_state_t *) vstate;

  state->iter = 0;
  return GSL_SUCCESS;
}

static int
conjugate_pr_iterate (void *vstate, gsl_multimin_function_fdf * fdf,
                      gsl_vector * x, double *f,
                      gsl_vector * gradient, gsl_vector * dx)
{
  conjugate_pr_state_t *state = (conjugate_pr_state_t *) vstate;

  gsl_vector *x1 = state->x1;
  gsl_vector *dx1 = state->dx1;
  gsl_vector *x2 = state->x2;
  gsl_vector *p = state->p;
  gsl_vector *g0 = state->g0;

  double pnorm = state->pnorm;
  double g0norm = state->g0norm;

  double fa = *f, fb, fc;
  double dir;
  double stepa = 0.0, stepb, stepc = state->step, tol = state->tol;

  double g1norm;
  double pg;

  if (pnorm == 0.0 || g0norm == 0.0)
    {
      gsl_vector_set_zero (dx);
      return GSL_ENOPROG;
    }

  /* Determine which direction is downhill, +p or -p */

  gsl_blas_ddot (p, gradient, &pg);

  dir = (pg >= 0.0) ? +1.0 : -1.0;

  /* Compute new trial point at x_c= x - step * p, where p is the
     current direction */

  take_step (x, p, stepc, dir / pnorm, x1, dx);

  /* Evaluate function and gradient at new point xc */

  fc = GSL_MULTIMIN_FN_EVAL_F (fdf, x1);

  if (fc < fa)
    {
      /* Success, reduced the function value */
      state->step = stepc * 2.0;
      *f = fc;
      gsl_vector_memcpy (x, x1);
      GSL_MULTIMIN_FN_EVAL_DF (fdf, x1, gradient);
      return GSL_SUCCESS;
    }

#ifdef DEBUG
  printf ("got stepc = %g fc = %g\n", stepc, fc);
#endif

  /* Do a line minimisation in the region (xa,fa) (xc,fc) to find an
     intermediate (xb,fb) satisifying fa > fb < fc.  Choose an initial
     xb based on parabolic interpolation */

  intermediate_point (fdf, x, p, dir / pnorm, pg,
                      stepa, stepc, fa, fc, x1, dx1, gradient, &stepb, &fb);

  if (stepb == 0.0)
    {
      return GSL_ENOPROG;
    }

  minimize (fdf, x, p, dir / pnorm,
            stepa, stepb, stepc, fa, fb, fc, tol,
            x1, dx1, x2, dx, gradient, &(state->step), f, &g1norm);

  gsl_vector_memcpy (x, x2);

  /* Choose a new conjugate direction for the next step */

  state->iter = (state->iter + 1) % x->size;

  if (state->iter == 0)
    {
      gsl_vector_memcpy (p, gradient);
      state->pnorm = g1norm;
    }
  else
    {
      /* p' = g1 - beta * p */

      double g0g1, beta;

      gsl_blas_daxpy (-1.0, gradient, g0); /* g0' = g0 - g1 */
      gsl_blas_ddot(g0, gradient, &g0g1);  /* g1g0 = (g0-g1).g1 */
      beta = g0g1 / (g0norm*g0norm);       /* beta = -((g1 - g0).g1)/(g0.g0) */

      gsl_blas_dscal (-beta, p);
      gsl_blas_daxpy (1.0, gradient, p);
      state->pnorm = gsl_blas_dnrm2 (p);
    }

  state->g0norm = g1norm;
  gsl_vector_memcpy (g0, gradient);

#ifdef DEBUG
  printf ("updated conjugate directions\n");
  printf ("p: ");
  gsl_vector_fprintf (stdout, p, "%g");
  printf ("g: ");
  gsl_vector_fprintf (stdout, gradient, "%g");
#endif

  return GSL_SUCCESS;
}


static const gsl_multimin_fdfminimizer_type conjugate_pr_type = {
  "conjugate_pr",               /* name */
  sizeof (conjugate_pr_state_t),
  &conjugate_pr_alloc,
  &conjugate_pr_set,
  &conjugate_pr_iterate,
  &conjugate_pr_restart,
  &conjugate_pr_free
};

const gsl_multimin_fdfminimizer_type
  * gsl_multimin_fdfminimizer_conjugate_pr = &conjugate_pr_type;