Mercurial > octave
view scripts/statistics/skewness.m @ 2311:2b5788792cad
[project @ 1996-07-11 20:18:38 by jwe]
author | jwe |
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date | Thu, 11 Jul 1996 20:18:38 +0000 |
parents | 5cffc4b8de57 |
children | 204cc7db6f4a |
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### Copyright (C) 1996 John W. Eaton ### ### This file is part of Octave. ### ### Octave 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, or (at your option) ### any later version. ### ### Octave 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 Octave; see the file COPYING. If not, write to the Free ### Software Foundation, 59 Temple Place - Suite 330, Boston, MA ### 02111-1307, USA. ## usage: skewness (x) ## ## If x is a vector of length N, return the skewness ## ## skewness (x) = N^(-1) std(x)^(-3) SUM_i (x(i)-mean(x))^3 ## ## of x. ## ## If x is a matrix, return a row vector containing the skewness for each ## column. function retval = skewness (x) ## Written by KH (Kurt.Hornik@ci.tuwien.ac.at) on Jul 29, 1994. if (nargin != 1) usage ("skewness (x)"); endif if (is_vector (x)) x = x - mean (x); if (! any (x)) retval = 0; else retval = sum (x .^ 3) / (length (x) * std (x) ^ 3); endif elseif (is_matrix (x)) [nr, nc] = size (x); x = x - ones (nr, 1) * mean (x); retval = zeros (1, nc); s = std (x); ind = find (s > 0); retval (ind) = sum (x (:, ind) .^ 3) ./ (nr * s (ind) .^ 3); else error ("skewness: x has to be a matrix or a vector."); endif endfunction