% m-file demonstrating diurnal variation of soil temperature
% Brian Hornbuckle, January 16, 2007.

clear;          % always important to do, make sure variables are reset

% --------- variables

z = 0.05;        % depth into soil, m 

t = linspace(0,48,1000);    % time variable, hours
                            % type "help linspace" at the command line to
                            % find out what linspace does

Tave = 15;      % average surface temperature, deg C

A = 5;          % amplitude, deg C

D = 0.05;       % damping depth, m

omega = pi/12;  % radian frequency, rad hour^-1

% -------------- calculations

T = Tave + A.*exp(-z./D).*sin(omega.*(t-8)-z./D);  % soil surface temperature

% -------- figures

figure(1)

plot(t,T); grid on;     % notice that you can put more than one command on a line
axis([0 48 5 25]);      % use this to make the figure look better (center on data)
xlabel('time, hours');
ylabel('soil surface temperature, \circC');
set(gca,'XTick',[0:4:48]);                    % put x tick marks every 4 hours

% for more practice, try to recreate Figure 2.5 in Campbell and Norman.