You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: evidence.m
    path of file: ./repos/pcm/matlab/lib/netlab3_3
    
    the code of the file until where you have to start completion: function [net, gamma, logev] = evidence(net, x, t, num)
%EVIDENCE Re-estimate hyperparameters using evidence approximation.

    
function [net, gamma, logev] = evidence(net, x, t, num)
%EVIDENCE Re-estimate hyperparameters using evidence approximation.
%
%	Description
%	[NET] = EVIDENCE(NET, X, T) re-estimates the hyperparameters ALPHA
%	and BETA by applying Bayesian re-estimation formulae for NUM
%	iterations. The hyperparameter ALPHA can be a simple scalar
%	associated with an isotropic prior on the weights, or can be a vector
%	in which each component is associated with a group of weights as
%	defined by the INDEX matrix in the NET data structure. These more
%	complex priors can be set up for an MLP using MLPPRIOR. Initial
%	values for the iterative re-estimation are taken from the network
%	data structure NET passed as an input argument, while the return
%	argument NET contains the re-estimated values.
%
%	[NET, GAMMA, LOGEV] = EVIDENCE(NET, X, T, NUM) allows the re-
%	estimation  formula to be applied for NUM cycles in which the re-
%	estimated values for the hyperparameters from each cycle are used to
%	re-evaluate the Hessian matrix for the next cycle.  The return value
%	GAMMA is the number of well-determined parameters and LOGEV is the
%	log of the evidence.
%
%	See also
%	MLPPRIOR, NETGRAD, NETHESS, DEMEV1, DEMARD
%

%	Copyright (c) Ian T Nabney (1996-2001)

errstring = consist(net, '', x, t);
if ~isempty(errstring)
  error(errstring);
end