function dzdt=fp1eq(t,z,a,c,f,omega)
%FP1EQ Forced pendulum equations (version 1).
%   DZDT=FP2EQ(T,Z,A,C,F,OMEGA) evaluates
%  
%     dx/dt = y
%     dy/dt = -A^2*sin(x) - C*y + F*sin(OMEGA*t)
%
%   at (x,y)=Z and t=T.

%   Francisco J. Beron-Vera, 2006/10/09

n=length(z);
dzdt=zeros(n,1);
x=z(1:2:end-1);
y=z(2:2:end);
dzdt=[y;-a^2*sin(x)-c*y+f*sin(omega*t)];
dzdt=reshape(dzdt,[n/2 2])';
dzdt=dzdt(:);