input-output covariance by input mean          [D*E x  D ]
%   dMds       ouput mean by input covariance                        [ E  x D*D]
%   dSds       output covariance by input covariance                 [E*E x D*D]
%   dVds       inv(s)*input-output covariance by input covariance    [D*E x D*D]
%
%   dMdi      output mean by inputs                                  [ E  x n*D]
%   dSdi      output covariance by inputs                            [E*E x n*D]
%   dVdi      inv(s) times input-output covari