spm_dcm_optimise.m

function [varargout] = spm_dcm_optimise(qE,qC,pE,pC,priorfun,varargin)
% Optimises the priors of a model (under Laplace approximation)
% FORMAT [rE,rC] = spm_dcm_optimise(qE,qC,pE,pC,priorfun,varargin)
%
% qE,qC    - posterior expectation and covariance of model
% pE,pC    - prior expectation and covariance of model
% priorfun - inline function that returns priors
%            {rE rC} = priorfun(varargin{:})
%
% rE,rC    - optimal priors defining a reduced model
%
%--------------------------------------------------------------------------
% This routine optimizes the prior covariance on the free parameters of any 
% model (DCM) under the Laplace approximation. In other words, it assumes 
% that the prior means are fixed and will maximise model evidence with 
% respect to the hyperparameters of a function that returns the prior 
% covariance. This optimization uses the reduced free-energy, based upon 
% the posterior and prior densities of the full model supplied. If the 
% prior covariance function is not specified, this routine will assume a 
% simple diagonal form with a single hyperparameter. In principle, this 
% routine can be used in a flexible and powerful way to emulate 
% hierarchical modeling by using suitable prior covariance functions with 
% unknown hyperparameters. The outputs are the prior moments (mean and 
% covariance) of the optimum model.
%__________________________________________________________________________
% Copyright (C) 2008-2011 Wellcome Trust Centre for Neuroimaging
 
% Karl Friston
% $Id: spm_dcm_optimise.m 4261 2011-03-24 16:39:42Z karl $
 
% Compute reduced log-evidence
%==========================================================================

% default prior function
%--------------------------------------------------------------------------
if nargin == 4
    priorfun    = inline('{v2, diag(exp(v1))}','v1','v2');
    varargin{1} = log(diag(pC));
    varargin{2} = pE;
end

varargout   = spm_argmax('spm_log_evidence',qE,qC,pE,pC,priorfun,varargin{:},6);
varargin{1} = varargout;
varargout   = priorfun(varargin{:});