EDITED
%Clear command window and workspace
clear
close all
clc
% Fitzhugh-Nagoma model parameters
e=0.01;
k=1:1:4; a=0.1;
i = 0.001;
figure(1);
hold on
u=zeros(500000,4);
v=zeros(500000,4);
t=zeros(100000,1);
% Initial conditions:
u(:)=0.6;
v(:)=0.0;
t(1)=0;
dt=0.001;
%==========================================================================
% Forvard Euler Method, for soluing the ODE
%==========================================================================
for i=1:1:500000
t(i+1)=t(i)+dt;
% u(i+1) = u(i)+ dt*((1/e)*((k(:)*u(i)*(u(i)-a)*(1-u(i)))-v(i)));
u(i+1,:) = u(i,:)+ dt.*((1/e).*((k.*(u(i,:).*(u(i,:)-a).*(1-u(i,:))))-v(i)));
v(i+1,:) = v(i,:)+ dt.*(u(i)-v(i));
end
% Getting the phase plot
figure(1);
upts=(-2:.05:2);
unullpts=(k(1).*upts.*(upts-a).*(1-upts));
vnullpts=upts;
plot(upts,unullpts,'black',upts,vnullpts,'black');
axis([-1 2 -1.5 5]);
hold on
plot(-u,-v,'b')
unullpts=(k(2).*upts.*(upts-a).*(1-upts));
vnullpts=upts;
plot(upts,unullpts,'m');
unullpts=(k(3).*upts.*(upts-a).*(1-upts));
vnullpts=upts;
plot(upts,unullpts,'r');
unullpts=(k(4).*upts.*(upts-a).*(1-upts));
vnullpts=upts;
plot(upts,unullpts,'g');
title('Nullcline Plot')
xlabel('u')
ylabel('v')
