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McDonald (2007) presented an approach to improving perturbation theory (PT)calculations of the dark matter power spectrum, with a derivation based on theidea of renormalization group flow with time. In spite of a questionableapproximation made in deriving it, subsequent comparisons by several groupsbetween the predictions of the resulting equation and N-body simulations showedremarkable improvement relative to "standard" PT (SPT) at similar order. Inthis brief note I show that the same final equation can be derived cleanly fromthe point of view not of flowing with time but with non-linear couplingstrength, i.e., gradually dialing the coupling from the trivial value zero tothe physical one. This understanding makes it clear how to extend the approachto higher order and other statistics. While I do not necessarily think thisapproach is best among the many, it may be interesting in that it contains aunique way of suppressing UV sensitivity. In passing I remind the reader ofreferences demonstrating that SPT works remarkably well without improvement(except near redshift zero, where, fortunately for SPT, there is very littlevolume in the Universe).

What the "simple renormalization group" approach to dark matter clustering really was