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: covGrid.m
    path of file: ./repos/hctsa/Toolboxes/gpml/cov
    
    the code of the file until where you have to start completion: function [K,Mx,xe] = covGrid(cov, xg, hyp, x, z, i)

% covGrid - Kronecker covariance function based on a grid.
%
% The grid g is represented by its p axes xg = {x1,x2,..xp}. An axis xi is of

    
function [K,Mx,xe] = covGrid(cov, xg, hyp, x, z, i)

% covGrid - Kronecker covariance function based on a grid.
%
% The grid g is represented by its p axes xg = {x1,x2,..xp}. An axis xi is of
% size (ni,di) and the grid g has size (n1,n2,..,np,D), where D=d1+d2+..+dp.
% Hence, the grid contains N=n1*n2*..*np data points. The axes do neither need
% to be sorted in any way nor do they need to be 1d i.e. ni>=1.
%
% The covGrid function can be used to expand the cell array xg into an expanded
% multivariate grid xe of size (N,D) via:
%     [xe,nx,Dx]  = covGrid('expand',xg);
% The operation can be reverted by:
%     xg = covGrid('factor',{xe,ng,Dg});
%
% The variables v={x,z} can either be a) grid indices or b) data points.
% a) The variable v has size (nv,1) and contains integers from [1,N]. Then
%    the datapoints are obtained as g2 = reshape(g,N,D); v = g2(v,:).
% b) The variable v has size (nv,D) and directly represents the data points.
% The mechanism works for x and z separately.
% 
% The resulting covariance matrix is given by:
%   K = kron( kron(...,K{2}), K{1} ) = K_p x .. x K_2 x K_1.
%
% The hyperparameters are:
% hyp = [ hyp_1
%         hyp_2
%          ..
%         hyp_p ],
%
% Copyright (c) by Hannes Nickisch and Andrew Wilson 2014-12-04.
%
% See also COVFUNCTIONS.M, INFGRID.M.

if nargin<2, error('Not enough parameters provided.'), end