**Thinking inside the box**, and kindly contributed to R-bloggers)

Earlier in the year, Romain and I did a bunch of initial work on a wrapper from

R to the

GNU GSL by way of our

Rcpp package for

seamless R and C++ integration. But other work kept us busy and this fell a

little to the side.

We have now found some time to finish this work for a first release, together

with a nicely detailed eleven page

package vignette.

As of today, the package is now a

CRAN package, and

Romain already posted a nice

announcement on his blog

and on

the rcpp-devel list.

So what does RcppGSL do? I gave the package

its own webpage here

as well and listed these points as key features of RcppGSL:

- templated vector and matrix classes: these are similar to Rcpp’s own

vector and matrix classes, but really are just smart pointers around the C

structure expected by the library - this means you can transfer data from R to your GSL-using programs in

pretty much the same way you would in other C++ programs using Rcpp—by

relying on the`Rcpp::as()`and`Rcpp::wrap()`

converterrs - at the C++ level you can use these GSL vectors in a more C++-alike

way (using eg`foo[i]`to access an element at index i) - yet at the same time you can just pass these vector and matrix objects

to the GSL functions expecting its C objects: thanks to some cleverness in

these classes they pass the right object on (see the example below) - we also provide the lightweight
*views*for vectors and matrices

as the GSL API uses these in many places.

Also provided is a simple example which is a simple implementation of a column norm (which we could easily

compute directly in R, but we are simply re-using an example from

Section 8.4.14

of the GSL manual):

#include <RcppGSL.h> #include <gsl/gsl_matrix.h> #include <gsl/gsl_blas.h> extern "C" SEXP colNorm(SEXP sM) { try { RcppGSL::matrix<double> M = sM; // create gsl data structures from SEXP int k = M.ncol(); Rcpp::NumericVector n(k); // to store results for (int j = 0; j < k; j++) { RcppGSL::vector_view<double> colview = gsl_matrix_column (M, j); n[j] = gsl_blas_dnrm2(colview); } M.free() ; return n; // return vector } catch( std::exception &ex ) { forward_exception_to_r( ex ); } catch(...) { ::Rf_error( "c++ exception (unknown reason)" ); } return R_NilValue; // -Wall }

This example function is implemented in an example package contained in the

RcppGSL package itself — so that users have a complete stanza to use in

their packages. This will then build a user package on Linux, OS X and Windows provided the

GSL is installed (and on Windows you have to do all the extra steps of

defining an environment variable pointing to and of course install Rtools to

build in the first place—Linux and OS X are so much easier for

development).

Another complete example is in the package itself and provides a faster

(compiled) alternative to the standard `lm()` function in R; this

example is the continuation of the same example I had in several versions of

my *Intro to HPC with R* tutorials and in the

Rcpp

package itself as an early example.

We will try to touch base with CRAN package authors using both GSL and Rcpp to see

how this can help them. The API in our package may well be incomplete, but

we are always happy to try to respond to requests for additional features

brought to our attention, preferably via the rcpp-devel list.

More information is on the

RcppGSL page.

Questions, comments etc should go to the

rcpp-devel mailing list

off the R-Forge page.

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**Thinking inside the box**.

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