function g =  lfmGradientSigmaH3AV(gamma1_p, gamma1_m, sigma2, t1, ...
    t2, preFactor, mode)

% LFMGRADIENTSIGMAH3AV Gradient of the function h_i(z) with respect \sigma.
% FORMAT
% DESC Computes the gradient of the function h_i(z) with respect to the
% length-scale of the input "force", \sigma.
% ARG gamma1 : Gamma value for first system.
% ARG gamma2 : Gamma value for second system.
% ARG sigma2 : length scale of latent process.
% ARG t1 : first time input (number of time points x 1).
% ARG t2 : second time input (number of time points x 1).
% ARG mode: indicates in which way the vectors t1 and t2 must be transposed
% RETURN g : Gradient of the function with respect to \sigma.
%
% COPYRIGHT : Mauricio Alvarez, 2010

% KERN

g = preFactor(1)*lfmavGradientSigmaUpsilonMatrix(gamma1_p,sigma2, t1,t2, mode) ...
    + preFactor(2)*lfmavGradientSigmaUpsilonMatrix(gamma1_m,sigma2, t1,t2, mode);
