function [ zTA ] = computeGradSL( X, z, GXTP )
%COMPUTE_ZTA Summary of this function goes here
%   Detailed explanation goes here

[N, K] = size(z);

zTP = bsxfun(@plus, z, -mean(z, 1))';
zTA =  2 * (zTP - (zTP * X) * GXTP) / N;

end