#define box_N         10 /* can be >= p */

#define box_P         3

#define box_NTRIES    1

static double box_x0[box_P] = { 0.0, 10.0, 20.0 };

static double box_epsrel = 1.0e-12;

static void

box_checksol(const double x[], const double sumsq,

              const double epsrel, const char *sname,

              const char *pname)

{

  size_t i;

  const double sumsq_exact = 0.0;

  const double box_x[box_P] = { 1.0, 10.0, 1.0 };

  gsl_test_rel(sumsq, sumsq_exact, epsrel, "%s/%s sumsq",

               sname, pname);

  for (i = 0; i < box_P; ++i)

    {

      gsl_test_rel(x[i], box_x[i], epsrel, "%s/%s i=%zu",

                   sname, pname, i);

    }

}

static int

box_f (const gsl_vector * x, void *params, gsl_vector * f)

{

  double x1 = gsl_vector_get(x, 0);

  double x2 = gsl_vector_get(x, 1);

  double x3 = gsl_vector_get(x, 2);

  size_t i;

  for (i = 0; i < box_N; ++i)

    {

      double ti = (i + 1.0) / 10.0;

      double fi = exp(-x1*ti) - exp(-x2*ti) - x3*(exp(-ti) - exp(-10.0*ti));

      gsl_vector_set(f, i, fi);

    }

  return GSL_SUCCESS;

}

static int

box_df (const gsl_vector * x, void *params, gsl_matrix * J)

{

  double x1 = gsl_vector_get(x, 0);

  double x2 = gsl_vector_get(x, 1);

  size_t i;

  for (i = 0; i < box_N; ++i)

    {

      double ti = (i + 1.0) / 10.0;

      double term1 = exp(-x1*ti);

      double term2 = exp(-x2*ti);

      double term3 = exp(-10.0*ti) - exp(-ti);

      gsl_matrix_set(J, i, 0, -ti*term1);

      gsl_matrix_set(J, i, 1, ti*term2);

      gsl_matrix_set(J, i, 2, term3);

    }

  return GSL_SUCCESS;

}

static gsl_multifit_function_fdf box_func =

{

  &box_f,

  &box_df,

  NULL,

  box_N,

  box_P,

  NULL,

  0,

  0

};

static test_fdf_problem box_problem =

{

  "box3d",

  box_x0,

  NULL,

  &box_epsrel,

  box_NTRIES,

  &box_checksol,

  &box_func

};