diff options
Diffstat (limited to 'gsl-1.9/statistics/wskew_source.c')
-rw-r--r-- | gsl-1.9/statistics/wskew_source.c | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/gsl-1.9/statistics/wskew_source.c b/gsl-1.9/statistics/wskew_source.c new file mode 100644 index 0000000..5dea05d --- /dev/null +++ b/gsl-1.9/statistics/wskew_source.c @@ -0,0 +1,59 @@ +/* statistics/wskew_source.c + * + * Copyright (C) 1996, 1997, 1998, 1999, 2000 Jim Davies, Brian Gough + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or (at + * your option) any later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + */ + +double +FUNCTION(gsl_stats,wskew) (const BASE w[], const size_t wstride, const BASE data[], const size_t stride, const size_t n) +{ + const double wmean = FUNCTION(gsl_stats,wmean)(w, wstride, data, stride, n); + const double wsd = FUNCTION(gsl_stats,wsd_m)(w, wstride, data, stride, n, wmean); + return FUNCTION(gsl_stats,wskew_m_sd)(w, wstride, data, stride, n, wmean, wsd); +} + +double +FUNCTION(gsl_stats,wskew_m_sd) (const BASE w[], const size_t wstride, + const BASE data[], + const size_t stride, const size_t n, + const double wmean, const double wsd) +{ + /* Compute the weighted skewness of a dataset */ + + long double wskew = 0; + long double W = 0; + + size_t i; + + /* find the sum of the cubed deviations, normalized by the sd. */ + + /* we use a recurrence relation to stably update a running value so + there aren't any large sums that can overflow */ + + for (i = 0; i < n; i++) + { + BASE wi = w[i * wstride]; + + if (wi > 0) { + const long double x = (data[i * stride] - wmean) / wsd; + W += wi ; + wskew += (x * x * x - wskew) * (wi / W); + } + } + + return wskew; +} + |