= Cubic stationary endpoint
{title2=$\int_0^\infty\cos(Na t^3)\,dt\sim\Gamma(1/3)\cos(\pi/6)/[3(Na)^{1/3}]$}
If the first two phase <derivatives> vanish at an endpoint but the third does not, an oscillatory contribution is concentrated on a width proportional to $N^{-1/3}$. For a smooth nonzero endpoint <oscillatory integral amplitude>, rescaling reduces the leading contribution to a cubic oscillatory integral. Its constant follows from the <Gamma function> Fourier integral. This is a degenerate form of the <stationary phase method>, and a quadratic formula is insufficient.
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