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: covPERiso.m
    path of file: ./repos/bads/gpml-matlab-v3.6-2015-07-07/cov
    
    the code of the file until where you have to start completion: function K = covPERiso(cov, hyp, x, z, i)

% Stationary periodic covariance function for an isotropic stationary covariance
% function k0 such as covMaterniso, covPPiso, covRQiso and covSEiso.
% Isotropic stationary means that the covariance function k0(x,z) depends on the
% data points x,z only through the squared distance
% dxz = (x-z)'*inv(P)*(x-z)
    
function is parameterized as:
%
% k(x,z) = k0(u(x),u(z)), u(x) = [sin(pi*x/p); cos(pi*x/p)]
%
% where the period p belongs to covPERiso and hyp0 belong to k0:
%
% hyp = [ log(p)
%         hyp0 ]
%
% The first hyperparameter of k0 is the log lengthscale hyp0(1) = log(ell).
% Note that for k0 = covSEiso and D = 1, a faster alternative is covPeriodic.
%
% Copyright (c) by Hannes Nickisch, 2013-10-15.
%
% See also COVFUNCTIONS.M.

nocov = false;                   % default case when no cov argument is provided
if nargin==0, cov = {@covSEiso}; nocov = true; end