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: pre_sphere.m
    path of file: ./repos/fieldtrip/external/dss
    
    the code of the file until where you have to start completion: function [params,X,means,wX,wM,dwM] = pre_sphere(params, X, dim)
% Spheres the data with the eigenvalue decomposition of the covariance matrix
%   [params,X,means,wX,wM,dwM] = pre_sphere(params, X, dim)
%     X    Data to be sphered
%     dim  Requested result data dimension
%     wX   Sphered data
%     wM   Sphering matrix
%     dwM  De-sphering matrix

% Copyright (C) 2004, 2005 DSS MATLAB package team (dss@cis.hut.fi).
% Distributed by Laboratory of Computer and Information Science,
% Helsinki University of Technology. http://www.cis.hut.fi/projects/dss/.
% $Id: pre_sphere.m,v 1.18 2005/11/30 08:20:52 jaakkos Exp $

if nargin<2

    
function [params,X,means,wX,wM,dwM] = pre_sphere(params, X, dim)
% Spheres the data with the eigenvalue decomposition of the covariance matrix
%   [params,X,means,wX,wM,dwM] = pre_sphere(params, X, dim)
%     X    Data to be sphered
%     dim  Requested result data dimension
%     wX   Sphered data
%     wM   Sphering matrix
%     dwM  De-sphering matrix

% Copyright (C) 2004, 2005 DSS MATLAB package team (dss@cis.hut.fi).
% Distributed by Laboratory of Computer and Information Science,
% Helsinki University of Technology. http://www.cis.hut.fi/projects/dss/.
% $Id: pre_sphere.m,v 1.18 2005/11/30 08:20:52 jaakkos Exp $

if nargin<2
    params.name = 'PCA sphering';
    params.description = 'Spheres the data with the eigenvalue decomposition of the covariance matrix.'; 
    return;
end