You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: circ_r.m
    path of file: ./repos/Image-Harmonization-Dataset-iHarmony4/Xue et al/dependency/CircStat2011f
    
    the code of the file until where you have to start completion: function r = circ_r(alpha, w, d, dim)
% r = circ_r(alpha, w, d)
%   Computes mean resultant vector length for circular data.
%

    
function r = circ_r(alpha, w, d, dim)
% r = circ_r(alpha, w, d)
%   Computes mean resultant vector length for circular data.
%
%   Input:
%     alpha	sample of angles in radians
%     [w		number of incidences 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, in radians (!)]
%     [dim  compute along this dimension, default is 1]
%
%     If dim argument is specified, all other optional arguments can be
%     left empty: circ_r(alpha, [], [], dim)
%
%   Output:
%     r		mean resultant length
%
% PHB 7/6/2008
%
% References:
%   Statistical analysis of circular data, N.I. Fisher
%   Topics in circular statistics, S.R. Jammalamadaka et al. 
%   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