That awkward moment, when the code written in matlab is easier to read and understand then tons of explanations:
Salakhudinov’s code of RBM

This code IMHO is a good argument when you need to explain someone that he/she  really needs to learn at least one language or tool with vectorization, no matter whether it is R, matlab, or numpy or theano in python.

I also want to note, that vectorization is not a silver bullet. For example, you can see Friedman's highly optimized fortran code of GLM (Generalized linear models)

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