Le 17/08/10 03:24, Dirk Eddelbuettel a écrit :
On 16 August 2010 at 19:43, Dirk Eddelbuettel wrote:
| Hi Christian,
|
| Thanks for your interest in Rcpp, and for posting here.
|
| On 16 August 2010 at 17:19, Christian Gunning wrote:
| | Dear list,
| |
| | I'm trying to use the ComplexVector class, and I'm having difficulty
| | with multiplication. I sugar multiplication, element-by-element
| | multiplication (no * operator for either), and using temporary
| | Rcomplex variables (don't really understand what I'm doing here).
|
| Well, NumericVector et al aren't really made for all possible math ops done
| on vectors, real or complex. They are first and foremost storage types. But
| for the math we do have Armadillo and RcppArmadillo. So in the short run, I
| would suggest the following two-step procedure:
|
| i) have a good look at Armadillo (http://arma.sf.net) and use the cx_mat
| or cx_vec types for mulitplication; write a small test program to see
| that everything works
|
| ii) use RcppArmadillo to from R via Rcpp / RcppArmadillo to this
| functionality
|
| | I was able to successfully import get("*") as an Rcpp::Function and do
| | the multiplication through R. Is this the best option for now?
|
| I am sure we can do better than this but I am not sure all pieces are in
| place just yet.
Looks like I wasn't all that far off. This builds:
library(inline)
code<- '
ComplexVector y1(i), y2(ii);
//arma::cx_vec a1(y1.begin(), y1.size(), false);
//arma::cx_vec a2(y2.begin(), y2.size(), false);
arma::cx_vec a1(y1.size());
arma::cx_vec a2(y2.size());
arma::cx_vec a3 = a1 * a2;
arma::cx_vec a4 = a1 + a2;
List z = List::create(a1, a2, a3, a4);
return z;
'
fun<- cxxfunction(signature(i="compex", ii="comples"), code,
plugin="RcppArmadillo")
The only trouble is that nobody has written the corresponding 'glue' code to
make
arma::cx_vec a1(y1.begin(), y1.size(), false);
cx_mat holds an array of std::complex<double>, not an array of Rcomplex.
so the compiler is unhappy.
However, Rcomplex and std::complex<double> have the same layout in
memory, so you are one reinterpret_cast away :
require( inline )
code<- '
ComplexVector y1(i), y2(ii);
arma::cx_vec a1( reinterpret_cast< std::complex<double>*
>(y1.begin()), y1.size(), false);
arma::cx_vec a2( reinterpret_cast< std::complex<double>*
>(y2.begin()), y2.size(), false);
arma::cx_vec a3 = a1 % a2; // element-wise multiplication in armadillo
arma::cx_vec a4 = a1 + a2;
List z = List::create(a1, a2, a3, a4);
return z;
'
fun<- cxxfunction(signature(i="complex", ii="complex"), code,
plugin="RcppArmadillo")
fun( 1:10*(1+1i), (1:10)*2+2i )
happen: create an Armadillo complex vector from an Rcpp::ComplexVector. We
can init by scalar size, what you'd need to insert for now is a simply (and
very pedestrian) copy-loop.
Hth, Dirk
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
http://romainfrancois.blog.free.fr
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