#define jennrich_N         10

#define jennrich_P         2

static double jennrich_x0[jennrich_P] = { 0.3, 0.4 };

static double jennrich_epsrel = 1.0e-7;

static void

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

                  const double epsrel, const char *sname,

                  const char *pname)

{

  size_t i;

  const double sumsq_exact = 1.243621823556148e+02;

  const double jennrich_x[jennrich_P] = { 2.578252139935855e-01,

                                          2.578252133471426e-01 };

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

               sname, pname);

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

    {

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

                   sname, pname, i);

    }

}

static int

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

{

  double x1 = gsl_vector_get(x, 0);

  double x2 = gsl_vector_get(x, 1);

  size_t i;

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

    {

      double ip1 = i + 1.0;

      double fi = 2.0*(i + 2.0) - (exp(x1*ip1) + exp(x2*ip1));

      gsl_vector_set(f, i, fi);

    }

  (void)params; /* avoid unused parameter warning */

  return GSL_SUCCESS;

}

static int

jennrich_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 < jennrich_N; ++i)

    {

      double ip1 = i + 1.0;

      gsl_matrix_set(J, i, 0, -ip1*exp(ip1*x1));

      gsl_matrix_set(J, i, 1, -ip1*exp(ip1*x2));

    }

  (void)params; /* avoid unused parameter warning */

  return GSL_SUCCESS;

}

static int

jennrich_fvv (const gsl_vector * x, const gsl_vector * v,

              void *params, gsl_vector * fvv)

{

  double x1 = gsl_vector_get(x, 0);

  double x2 = gsl_vector_get(x, 1);

  double v1 = gsl_vector_get(v, 0);

  double v2 = gsl_vector_get(v, 1);

  size_t i;

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

    {

      double ip1 = i + 1.0;

      double term1 = exp(ip1*x1);

      double term2 = exp(ip1*x2);

      gsl_vector_set(fvv, i, -ip1*ip1*(v1*v1*term1 + v2*v2*term2));

    }

  (void)params; /* avoid unused parameter warning */

  return GSL_SUCCESS;

}

static gsl_multifit_nlinear_fdf jennrich_func =

{

  jennrich_f,

  jennrich_df,

  jennrich_fvv,

  jennrich_N,

  jennrich_P,

  NULL,

  0,

  0,

  0

};

static test_fdf_problem jennrich_problem =

{

  "jennrich",

  jennrich_x0,

  NULL,

  NULL,

  &jennrich_epsrel,

  &jennrich_checksol,

  &jennrich_func

};