Integral of exponential function with polynomial argument I am looking for an effcient way to evaluate
$$
I = \int_{-\infty}^\infty dx\  e^{-ax+bx^2+cx^4}\\
\text{where } a,b,c \in \mathbb{R}^+
$$
I have already read about a solution involving the series expansion of the exponential here Computing the integrals of the form $\exp(P(x))$, $P(x)$ a polynomial but I am looking for something computationally more efficient...
Any help is greatly appreciated! 

The answer to your question is very simple. In fact the integral does not converge as $c>0$.
