function Oct30()
% let z1(t) = x(t) and z2(t) = (d/dt)x(t). It follows that 
%         [ z1(t) ]    [        z2(t)       ]
%    d/dt [       ]  = [                    ]
%         [ z2(t) ]    [ -A*z2(t) - B*z1(t) ]

% So this is the slope function:

function zp = f(t,z,A,B)
n = length(z)/2;
zp = [z(n+1:2*n) ; -A*z(n+1:2*n)-B*z(1:n)]

% And the initial condition is z0 = [x0;xp0];