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: meanGPexact.m
    path of file: ./repos/hctsa/Toolboxes/gpml/mean
    
    the code of the file until where you have to start completion: function A = meanGPexact(mean,cov,x,y, hypz,z,i)

% Mean function being the predictive mean of a GP model:
%
% m(z) = posterior mean of GP at location z as given by
% m(z) = gp(hyp,@infExact,mean,cov,@likGauss,x,y, z) where
% hyp.mean = hyp_mean; hyp.lik = log(sn); hyp.cov = hyp.cov;
%
% The hyperparameters are:

    
function A = meanGPexact(mean,cov,x,y, hypz,z,i)

% Mean function being the predictive mean of a GP model:
%
% m(z) = posterior mean of GP at location z as given by
% m(z) = gp(hyp,@infExact,mean,cov,@likGauss,x,y, z) where
% hyp.mean = hyp_mean; hyp.lik = log(sn); hyp.cov = hyp.cov;
%
% The hyperparameters are:
%
% hypz = [ hyp_cov
%          log(sn)
%          hyp_mean ]
%
% where hyp_cov are the covariance function hyperparameters, sn is the
% noise variance of the Gaussian likelihood and hyp_mean are the mean
% function hyperparameters.
%
% Copyright (c) by Hannes Nickisch, 2014-11-01.
%
% See also MEANFUNCTIONS.M and MEANGP.M.

if nargin<4, error('GP must be specified.'), end