wk = gsl_multifit_linear_alloc (design->size1, design->size2);
rc = gsl_multifit_linear (design, Y, param_estimates,
cache->cov, &(cache->sse), wk);
wk = gsl_multifit_linear_alloc (design->size1, design->size2);
rc = gsl_multifit_linear (design, Y, param_estimates,
cache->cov, &(cache->sse), wk);