In R, we can check whether a vector (e.g., vec1=c(1+1i,2)) contains complex numbers using is.complex (e.g., is.complex(vec1)). I wonder what the equivalent function is in RcppArmadillo?
And how to extract the real part of each element in the vector in RcppArmadillo, like Re(vec1) in R?
For extracting the real and imaginary parts, you can use the arma::real() and arma::imag() functions. Alternatively you can use the sugar function Rcpp::Re() and Rcpp::Im():
// [[Rcpp::depends(RcppArmadillo)]]
#include <RcppArmadillo.h>
// [[Rcpp::export]]
arma::vec getRe(arma::cx_vec x) {
return arma::real(x);
}
// [[Rcpp::export]]
Rcpp::NumericVector getIm(Rcpp::ComplexVector x) {
return Rcpp::Im(x);
}
/*** R
set.seed(42)
N <- 5
vec <- complex(5, rnorm(5), rnorm(5))
t(getRe(vec))
#> [,1] [,2] [,3] [,4] [,5]
#> [1,] -0.9390771 -0.04167943 0.8294135 -0.4393582 -0.3140354
Re(vec)
#> [1] -0.93907708 -0.04167943 0.82941349 -0.43935820 -0.31403543
getIm(vec)
#> [1] -2.1290236 2.5069224 -1.1273128 0.1660827 0.5767232
Im(vec)
#> [1] -2.1290236 2.5069224 -1.1273128 0.1660827 0.5767232
*/
If you were to use getRe(arma::vec x) above, you would get:
Warning message:
In getRe(vec) : imaginary parts discarded in coercion
You just cannot put complex numbers in an object that is not meant to store them. This is a consequence of C++ being a strongly typed language. So there is no need for an analogue to is.complex().
See the Armadillo documentation for further reference.