function g = demgpot(x, mix)%DEMGPOT Computes the gradient of the negative log likelihood for a mixture model.%%	Description%	This function computes the gradient of the negative log of the%	unconditional data density P(X) with respect to the coefficients of%	the data vector X for a Gaussian mixture model.  The data structure%	MIX defines the mixture model, while the matrix X contains the data%	vector as a row vector. Note the unusual order of the arguments: this%	is so that the function can be used in DEMHMC1 directly for sampling%	from the distribution P(X).%%	See also%	DEMHMC1, DEMMET1, DEMPOT%%	Copyright (c) Ian T Nabney (1996-2001)% Computes the potential gradienttemp = (ones(mix.ncentres,1)*x)-mix.centres;temp = temp.*(gmmactiv(mix,x)'*ones(1, mix.nin));% Assume spherical covariance structureif ~strcmp(mix.covar_type, 'spherical')  error('Spherical covariance only.')endtemp = temp./(mix.covars'*ones(1, mix.nin));temp = temp.*(mix.priors'*ones(1, mix.nin));g = sum(temp, 1)/gmmprob(mix, x);