Laplace endpoint estimate ($\frac{a(b)e^{\lambda \varphi (b)}}{\lambda \varphi \prime (b)}$)

If a real smooth phase has its strict maximum at the upper endpoint $b$ and $\varphi \prime (b)>0$, then ${\int }_a^{b}a(t)e^{\lambda \varphi (t)}dt\sim a(b)e^{\lambda \varphi (b)}/(\lambda \varphi \prime (b))$. The endpoint coordinate $b-t$ has scale $1/\lambda$. At a nondegenerate stationary endpoint the scale is instead ${\lambda }^{-1/2}$ and the leading contribution is half a Gaussian integral.