|, bounds etc. will be
% ignored. 
%
%   penm.NY = 3; 
%
% * cell array of length |NY| with a nonzero pattern of each of the matrix 
%   variables. Each matrix will be vectorized and all its nonzeros in
%   the lower triangle will be considered as variables, the rest as constant
%   zeros. The utility '...' can
%   generate back the matrix and the exact position of the variable ...
%
%   penm.Y{1} = ones(3); 
%   penm.Y{2} = spones(sprandsym(5,0.3)); 
%   penm.Y{3} = spones(sprand(6,6,0.2));
%