RcppDE 0.1.0

December 13, 2010
By

(This article was first published on Thinking inside the box , and kindly contributed to R-bloggers)

A new package RcppDE has been uploaded in a first version 0.1.0 to
CRAN.
It provides differential evolution optimisation—a variant of stochastic
optimisation that is similar to genetic algorithms but particularly suitable
for the floating-point representations common in numerical optimisation.
It builds of on the nice
DEoptim package by
Ardia et al, but reimplements the algorithm in C++ (rather than C) using a
large serving of
Rcpp and
RcppArmadillo.

I worked on this on for a few evenings and weekends in October and November
and then spent a few more evenings writing a
paper / vignette
(which is finished as a very first draft now)
about it. This was an interesting and captivating problem as I had worked on
genetic algorithms going back quite some time to the beginning and then again
the end of graduate school (and traces of that early work are near the bottom of my
presentations page).
So what got me started?
DEoptim is a really
nice package, but it is implemented in old-school
C.
There is nothing wrong with that per se, but at the same time that I was
wrestling with GAs, I also taught myself
C++ which, to put it
simply, offers a few more choices to the programmer. I like having those choices.

And with all the work that
Romain and I have put into
Rcpp, I was curious
how far I could push this cart if I were to move it along.
I made a bet with myself starting from the old saw shorter, easier,
faster: pick any two
. Would it be possible to achieve all three of
these goals?

DEoptim, and I take
version 2.0-7 as my reference point here, is pretty efficiently yet
verbosely coded. Copying a vector takes a loop with an assignment for each
element, copying a matrix does the same using two loops. Replacing that with
a single statement in C++ is pretty easy.
We also have a few little optimisations behind the scenes here and there in
Rcpp: would all
that be enough to move the needle in terms of performance?
And the same time,
DEoptim is also full
of the uses of the old R API which we often point to in the
Rcpp documentation
so fixing readibility should be a relatively low-hanging fruit.

To cut a long story short, I was able to reduce code size quite
easily by using a combination of
C++ and
Rcpp idioms. I was
also able to get to faster: the
paper / vignette
demostrates consistent speed improvements on all setups that I tested (three
standard functions on three small and three larger parameter vectors). More
important speed gains were achieved by allowing use of objective functions
that are written in C++
which again is both possible and easy thanks to
Rcpp.

That leaves easier to prove: adding compiled objective functions is
one indication; further proof could be provided by, say, moving the inner
loop to parallel execution thanks to Open MP
which I may attempt over the next few months. So far I’d like to give myself about
half a point here. So not quite yet shorter, easier, faster: pick any three, but working on it.

Over the next few days I may try to follow up with a blog post or two
contrasting some code examples and maybe showing a chart from the vignette.

To leave a comment for the author, please follow the link and comment on their blog: Thinking inside the box .

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