How do I use pi in RcppEigen?
I am very new to Rcpp
, or rather, RcppEigen
and am struggling with how to use pi
as a constant in my code. The code runs many times in the MCMC algorithm, so any speed improvement would be ideal. Currently I am passing pi every time I call the function like in the following code:
require(RcppEigen)
require(inline)
I.Cpp <- "
using Eigen::Map;
using Eigen::MatrixXd;
using Eigen::VectorXd;
using Rcpp::NumericVector;
const Map<MatrixXd> delta(as<Map<MatrixXd> >(delta0));
const Map<VectorXd> d(as<Map<VectorXd> >(DD));
const Rcpp::NumericVector tpi(pie);
double pi = tpi[0];
const MatrixXd I = delta.transpose() * d.asDiagonal() * pi * pi;
return wrap(I);
"
I.cpp <- cxxfunction(signature(delta0 = "matrix", DD = "numeric", pie = "numeric"), I.Cpp, plugin = "RcppEigen")
delta0 <- matrix(rnorm(25), 5)
DD <- rnorm(5)
I.cpp(delta0, DD, pi) # this piece of code gets called multiple times?
My question is, how can I use a constant pi
internally RcppEigen
without passing it in on every call I.cpp
?
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First of all grep for pi
in /usr/share/R/include/
, and you will find for example
#define M_PI 3.141592653589793238462643383280 /* pi */
so you have where R is used, for example here with Rcpp and RcppEigen.
Example:
R> getpi <- cppFunction('double twopi() { return M_PI; } ')
R> getpi()
[1] 3.142
R> print(getpi(), digits=20)
[1] 3.141592653589793116
R>
I'm sure it's in the headlines too. [Checks: Yup, starting at math.h
. ] Perhaps several times. Grepping through other sources can also be fruitful.
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