#define lin1_N         11  /* can be anything >= p */

#define lin1_P         5

#define lin1_NTRIES    3

static double lin1_x0[lin1_P] = { 1.0, 1.0, 1.0, 1.0, 1.0 };

static double lin1_epsrel = 1.0e-10;

static void

lin1_checksol(const double x[], const double sumsq,

              const double epsrel, const char *sname,

              const char *pname)

{

  size_t i;

  const double sumsq_exact = (double) (lin1_N - lin1_P);

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

               sname, pname);

  for (i = 0; i < lin1_P; ++i)

    {

      gsl_test_rel(x[i], -1.0, epsrel, "%s/%s i=%zu",

                   sname, pname, i);

    }

}

static int

lin1_f (const gsl_vector * x, void *params, gsl_vector * f)

{

  size_t i, j;

  for (i = 0; i < lin1_N; ++i)

    {

      double fi = 0.0;

      for (j = 0; j < lin1_P; ++j)

        {

          double xj = gsl_vector_get(x, j);

          double Aij = (i == j) ? 1.0 : 0.0;

          Aij -= 2.0 / lin1_N;

          fi += Aij * xj;

        }

      fi -= 1.0;

      gsl_vector_set(f, i, fi);

    }

  return GSL_SUCCESS;

}

static int

lin1_df (const gsl_vector * x, void *params, gsl_matrix * J)

{

  size_t i, j;

  for (i = 0; i < lin1_N; ++i)

    {

      for (j = 0; j < lin1_P; ++j)

        {

          double Jij = (i == j) ? 1.0 : 0.0;

          Jij -= 2.0 / lin1_N;

          gsl_matrix_set(J, i, j, Jij);

        }

    }

  return GSL_SUCCESS;

}

static gsl_multifit_function_fdf lin1_func =

{

  &lin1_f,

  &lin1_df,

  NULL,

  lin1_N,

  lin1_P,

  NULL,

  0,

  0

};

static test_fdf_problem lin1_problem =

{

  "linear_full",

  lin1_x0,

  NULL,

  &lin1_epsrel,

  lin1_NTRIES,

  &lin1_checksol,

  &lin1_func

};