this eigenvector 
%   specifies the division. To implement this algorithm,
%   |BiMat| first converts the bipartite matrix into its unipartite version
%   and the initial step.
%
% In addition to optimize the standard modularity @Q_b@ \bimat also evaluates
% (after optimizing @Q_b@) an a posteriori measure of modularity @Q_r@
% introduced in <http://f1000research.com/articles/2-130/v3 Poisot 2013> and defined as:
% <latex>
% \begin{equation}
% Q_r = 2\times\frac{W}{E}-1 %% This version returns val