function [U,V]=sample_field2(X,Y) % sample call % phase_portrait('sample_field2',-3:0.1:3,-3:0.1:3,200,0.03,30) U=sin(X.^3-2*X.^2-3*X+1-Y.^2); V=cos(Y.^3-2*Y.^2-3*Y+1-X.^2);