rhs_vdp.m

function f = rhs_vdp(t,x,xd);
% RHS of ODE for Vanderpol's equation
%   xdd + mu*(x^2-1)*xd + k*x = 0

mu = 4;         % mass
k = 1;        % spring constant

f = - mu*(x^2-1)*xd - k*x;