static int
set (void *vstate, gsl_multifit_function_fdf * fdf, gsl_vector * x, gsl_vector * f, gsl_matrix * J, gsl_vector * dx, int scale)
{
  lmder_state_t *state = (lmder_state_t *) vstate;

  gsl_matrix *r = state->r;
  gsl_vector *tau = state->tau;
  gsl_vector *diag = state->diag;
  gsl_vector *work1 = state->work1;
  gsl_permutation *perm = state->perm;

  int signum;

  /* Evaluate function at x */
  /* return immediately if evaluation raised error */
  {
    int status = GSL_MULTIFIT_FN_EVAL_F_DF (fdf, x, f, J);
    if (status)
      return status;
  }

  state->par = 0;
  state->iter = 1;
  state->fnorm = enorm (f);

  gsl_vector_set_all (dx, 0.0);

  /* store column norms in diag */

  if (scale)
    {
      compute_diag (J, diag);
    }
  else
    {
      gsl_vector_set_all (diag, 1.0);
    }

  /* set delta to 100 |D x| or to 100 if |D x| is zero */

  state->xnorm = scaled_enorm (diag, x);
  state->delta = compute_delta (diag, x);

  /* Factorize J into QR decomposition */

  gsl_matrix_memcpy (r, J);
  gsl_linalg_QRPT_decomp (r, tau, perm, &signum, work1);

  gsl_vector_set_zero (state->rptdx);
  gsl_vector_set_zero (state->w);

  /* Zero the trial vector, as in the alloc function */

  gsl_vector_set_zero (state->f_trial);

#ifdef DEBUG
  printf("r = "); gsl_matrix_fprintf(stdout, r, "%g");
  printf("perm = "); gsl_permutation_fprintf(stdout, perm, "%d");
  printf("tau = "); gsl_vector_fprintf(stdout, tau, "%g");
#endif

  return GSL_SUCCESS;
}