gsl_vector_set (&(xty.vector), 0, tmp);
tmp *= tmp / gsl_vector_get (cache->ssx, 0);
gsl_vector_set (cache->ss_indeps, 0, tmp);
gsl_vector_set (&(xty.vector), 0, tmp);
tmp *= tmp / gsl_vector_get (cache->ssx, 0);
gsl_vector_set (cache->ss_indeps, 0, tmp);