// [[Rcpp::plugins(cpp11)]]

// [[Rcpp::depends(RcppParallel)]]

#include <Rcpp.h>

#include <RcppParallel.h>

using namespace Rcpp;

using namespace RcppParallel;

struct Transformer : public Worker {

const RMatrix<double> input;

RMatrix<double> output;

Transformer(const NumericMatrix input, NumericMatrix output)

: input(input), output(output) {}

void operator()(std::size_t begin, std::size_t end) {

std::transform(input.begin() + begin, input.begin() + end,

output.begin() + begin, [](double x) {

return 1 / (1 + x * x);

});

}

};

// [[Rcpp::export]]

NumericMatrix par_transform (NumericMatrix x) {

NumericMatrix output(x.nrow(), x.ncol());

Transformer transformer(x, output);

parallelFor(0, x.length(), transformer);

return output;

}