function [J] = jacsys(x)
%calculates jacobi of 2 x 2 system
%Turner p.46, x(1)=x, x(2)=y
J(1,1) = 8*x(1);
J(1,2) = 2*x(2);
J(2,1) = 2*x(1)*x(2)^3;
J(2,2) = 3*x(1)^2*x(2)^2;
return