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: dss_sphere.m
    path of file: ./repos/fieldtrip/external/dss/orig
    
    the code of the file until where you have to start completion: function [V,dV] = dss_sphere(X, dim, symmetric)
%   [V,dV] = dss_sphere(X)
%   [V,dV] = dss_sphere(X, dim)
%   [V,dV] = dss_sphere(X, dim, symmetric)
%     X          Data to be sphered

    
function [V,dV] = dss_sphere(X, dim, symmetric)
%   [V,dV] = dss_sphere(X)
%   [V,dV] = dss_sphere(X, dim)
%   [V,dV] = dss_sphere(X, dim, symmetric)
%     X          Data to be sphered
%     dim        Requested result data dimension, 0 for no reduction
%     symmetric  Boolean, perform symmetric sphering
%     V          Sphering matrix
%     dV         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/.
% $Id$

% Treshold for eigenvalues that are treated zero
tresholdEig=1e-9;
% Treshold for maximum covariance for treating data already sphered
tresholdSphered=1e-9;

if nargin>=2 & dim~=0; dim = min(dim, size(X, 1));
else; dim = size(X, 1);
end