function dy = lotka_volt(t,y)
% define the system y1'=by1-cy1y2; y2'=-dy2+cy1y2; due to Lotka_Volterra 
    b=1; c=1; d=10;
    dy = zeros(2,1);    % a column vector
    dy(1) = b*y(1) - c*y(1)*y(2);
    dy(2) = -d*y(2) + c*y(1)*y(2);
return;