Estimation of Potential Evapotranspiration using Mcguinnes Bordne formulation

This is a simple function that estimates potential evapotranspiration with minimum data requirement.

% *************************************************************
% Code written by Pankaj Dey, PhD student in Indian Institute of Science,
% Bangalore
%****************************************************************
% This function is use to calculate daily potential evapotranspiration
% using Mcguinnes Bordne formulation.
%
% Input:
% lat: latitude of the place in decimal degrees.
% date: date array in the following format
%
%For example: Col.1 Col.2 Col.3
% Year Month Day
%
% date= 1904 3 1
% 1905 3 1
%
% t_max: maximum daily temperature in degree celsius
% t_min: minimum daily temperature in degree celsius
%
% Output: pet_mm_per_day is daily potential evapotranspiration in fourth
% column. The first three columns indicate year, month and day of the
% observation respectively.