es.ipynb: In Gaussian, do you multiply by sigma**2 intentionally?

Hi,

In [`es.ipynb`](https://github.com/karpathy/randomfun/blob/master/es.ipynb) I noticed that your four Gaussian functions don't have braces around `sigma**2`, looks like this:

`G1 = np.exp(-((X-mux)**2+(Y-muy)**2)/2.0*sigma**2)`
instead of:
`G1 = np.exp(-((X-mux)**2+(Y-muy)**2)/2.0*(sigma**2))`

So you actually multiply by sigma**2 in the exponential function, instead of dividing as you would in a normal Gaussian function.

This doesn't have any consequence for the toy example, I'm just curious if it was intentional (there could be a reason of doing this that I'm not aware of)?

Open es.ipynb and inspect the four Gaussian definitions, especially the sigma**2 expression in G1. Verify the intended Gaussian formula and whether the current multiplication is deliberate; done means resolving the question and correcting or documenting the notebook consistently.

Written by the indexing model from the issue text.