It does what it says. Its vectorized, well coded, with good help, some error checks (ok, it does not check for sigma<0, nor worry about the shapes of its arguments), it has default values for the parameters, an H1 line, a reference to wikipedia. These are all things I like very much to see.
In my obsessive drive for completeness, I'd want to see also tools for the pdf, cdf, and inverse cdf. I wanted to rate this about a 4.5 as is.