function y = L1(r)

M1 = 1.991e30;
M2 = 5.98e24;
R = 149597870700;

y = M1 / (R - r)^2 - M2 / r^2 - (M1 / (M1 + M2) * R - r) * (M1 + M2) / R^3;
