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: covarxyt_pv.m
    path of file: ./repos/matlab_owc/matlab_codes
    
    the code of the file until where you have to start completion: 
% function [a] = covarxyt_pv(x1,x2,gs,ts,q,phi,pv)
%
% Outpu
    
function [a] = covarxyt_pv(x1,x2,gs,ts,q,phi,pv)
%
% Output:
% a 	m*n  unscaled Gaussian covariance function
%
% Input:
% x1	m*4 model grid, col 1+2+3+4 are lat, long, date, depth respectively
% x2	n*4 data grid, col 1+2+3+4 are lat, long, date, depth respectively
% ts	scalar, horizontal latitude scale  (degrees)
% gs    scalar, horizontal longitude scale (degrees)
% q	scalar, time scale  (years)
% phi   scalar cross isobaric scale (for depth depend