function yp=equation(x,y);
%
%BBI 99
global K fi fo
RC=25/(2*pi*fo);   %濾波器的時間常數
yp(1)=y(2);
yp(2)=K/RC*sin(2*pi*fi*x).*cos(2*pi*po*x+y(1))-y(2)/RC;
v=version;v=v(1);
if strcmp(v,'5');yp=yp';end;