%%% phase.m: to run this script, at the matlab prompt type
%%% phase
%%%
%%% this script solves the system of ODEs defined in equ.m
%%% (a pendulum with friction = eps * velocity) and then makes 
%%% a Phase Plane Plot of the solution. To vary the friction, change
%%% the constant eps in equ.m
%%%
%%% requires the file equ.m

t0 = 0;		% Starting time
tfinal = 15;	% Ending time
tol = 1.e-3;	% Accuracy
trace = 1;	% trace
y0 = [2 2]';	% Define initial conditions.
tspan = [t0 tfinal];
[t, y] = ode23('equ',tspan,y0);			% Solve ODE
plot(y(:,1),y(:,2),'g'), title('Phase Plane Plot'),	% Plot solution
	xlabel('u-axis'), ylabel('v-axis')