function y=volterra(t,u) 
% function for the volterra-lotka population model
% [t,U]=my_ode('volterra',[0 50],[.5;.3],1e-2);  
% plot(t,U) 
% plot(U(:,1),U(:,2))

a=.5; b=1; c=.2; d=1; 
y=zeros(2,1);
y(1)= a*u(1)-b*u(1)*u(2); 
y(2)=-c*u(2)+d*u(1)*u(2); 


