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

% Gabor covariance function with length scales ell and periods p. The covariance
% function is parameterized as:
%
% k(x,z) = h(x-z), h(t) = exp(-sum(t.^2./(2*ell.^2)))*cos(2*pi*sum(t./p)).
%
% The hyperparameters are:
%
% hyp = [ log(ell_1)
%         log(ell_2)
%          ..
%         log(ell_D)
%         log(p_1)
%         log(p_2)
%          ..
%         log(p_D) ]
%
% For more help on design of covariance functions, try "help covFunctions".
%
% Note that covSM implements a weighted sum of Gabor covariance functions, but
% using an alternative (spectral) parameterization.

    
function K = covGaborard(hyp, x, z, i)

% Gabor covariance function with length scales ell and periods p. The covariance
% function is parameterized as:
%
% k(x,z) = h(x-z), h(t) = exp(-sum(t.^2./(2*ell.^2)))*cos(2*pi*sum(t./p)).
%
% The hyperparameters are:
%
% hyp = [ log(ell_1)
%         log(ell_2)
%          ..
%         log(ell_D)
%         log(p_1)
%         log(p_2)
%          ..
%         log(p_D) ]
%
% For more help on design of covariance functions, try "help covFunctions".
%
% Note that covSM implements a weighted sum of Gabor covariance functions, but
% using an alternative (spectral) parameterization.
%
% Copyright (c) by Hannes Nickisch, 2014-09-26.
%
% See also COVFUNCTIONS.M, COVGABORISO, COVSM.M.

if nargin<2, K = '2*D'; return; end