function S = goverlap(g1, g2)
Ex=gprod_1D(g1.x0,g1.alpha,g2.x0,g2.alpha);
Ey = gprod_1D(g1.y0, g1.alpha, g2.y0, g2.alpha);
Ez=gprod_1D(g1.z0,g1.alpha,g2.z0,g2.alpha);
S=Ex*Ey*Ez*sqrt(pi/(g1.alpha + g2.alpha))^3*g1.N*g2.N;