function dy = vdpeq(t,y)
% This is the corresponding "system" file for vanderpol.m. You should not
% need to modify this code in order to do the problem. However, this would
% be a good template as you start to write your own solvers.
%
% This code is called by the "solver" and is provided with some
% information. It is given the current location of the system (x,dxdt)
% which comes in as a column vector and the current time. It will return
% the derivative vector for this point, dy.
global e % You declare that the variable 'e' will be valid here
% which allows you to only have to set the value for epsilon once.
dy = zeros(2,1); % creates the derivative vector
dy(1) = y(2); % solves for the first of the system of equations.
% In the Van der Pol case this is just setting dxdt = y
dy(2) = -y(1)-e*y(2).*(y(1).^2-1); % solves for the second of the equations.
% In the Van der Pol case dydt = -x-epsilon*y*(x^2-1)