> When number of input data is 1, I think it is > more reasonable to say standard deviation is 0 instead of nan. > > double sd = gsl_stats_sd(data, 1, 1);
Do you want gsl_stats_sd_with_fixed_mean instead of gsl_stats_sd? http://www.gnu.org/software/gsl/manual/html_node/Mean-and-standard-deviation-and-variance.html - Rhys
