# [Rcpp-devel] Multiplication of ComplexVector?

Dirk Eddelbuettel edd at debian.org
Tue Aug 17 02:43:17 CEST 2010

```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.

Cheers, Dirk

| Thanks,
| Christian Gunning
| University of New Mexico
|
| // doesn't work
| SEXP rcpp_hello_world(SEXP i, SEXP ii){
|     using namespace Rcpp ;
|
|     ComplexVector y1(i), y2(ii);
|     int n(y1.size()), j;
|     ComplexVector y3(n), y4(n);
|     y3 = y1 * y2;  // no operator
|     for (j = 0; j++; j<n) {
|         y4[j] = y1[j] + y2[j]; // no operator
|     }
|     List z            = List::create( y1, y2, y3) ;
|     return z ;
| }
|
| // does work, doing multiplication in R
| SEXP mymult(SEXP input1, SEXP input2) {
|     Rcpp::Environment base("package:base");
|     Rcpp::Function funbase = base["get"];
|     SEXP funbase1 = funbase("*");
|     Rcpp::Function funmult(funbase1);
|     Rcpp::ComplexVector xxa = funmult(input1, input2);
|     return xxa;
| }
|
| SEXP rcpp_hello_world(SEXP i, SEXP ii){
|     using namespace Rcpp ;
|     ComplexVector y3( mymult(i, ii) );
|     return y3 ;
| }
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--
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com
```