Code covered by the BSD License

# Circular Statistics Toolbox (Directional Statistics)

### Philipp Berens (view profile)

08 Apr 2006 (Updated )

Compute descriptive and inferential statistics for circular or directional data.

### Editor's Notes:

This file was selected as MATLAB Central Pick of the Week

circ_std(alpha, w, d, dim)
```function [s s0] = circ_std(alpha, w, d, dim)
% s = circ_std(alpha, w, d, dim)
%   Computes circular standard deviation for circular data
%   (equ. 26.20, Zar).
%
%   Input:
%     alpha	sample of angles in radians
%     [w		weightings in case of binned angle data]
%     [d    spacing of bin centers for binned data, if supplied
%           correction factor is used to correct for bias in
%           estimation of r]
%     [dim  compute along this dimension, default is 1]
%
%     If dim argument is specified, all other optional arguments can be
%     left empty: circ_std(alpha, [], [], dim)
%
%   Output:
%     s     angular deviation
%     s0    circular standard deviation
%
% PHB 6/7/2008
%
% References:
%   Biostatistical Analysis, J. H. Zar
%
% Circular Statistics Toolbox for Matlab

% By Philipp Berens, 2009
% berens@tuebingen.mpg.de - www.kyb.mpg.de/~berens/circStat.html

if nargin < 4
dim = 1;
end

if nargin < 3 || isempty(d)
% per default do not apply correct for binned data
d = 0;
end

if nargin < 2 || isempty(w)
% if no specific weighting has been specified
% assume no binning has taken place
w = ones(size(alpha));
else
if size(w,2) ~= size(alpha,2) || size(w,1) ~= size(alpha,1)
error('Input dimensions do not match');
end
end

% compute mean resultant vector length
r = circ_r(alpha,w,d,dim);

s = sqrt(2*(1-r));      % 26.20
s0 = sqrt(-2*log(r));    % 26.21

```