"inner_product" was not declared in this scope - r

Question

Hi I am new to rcpp and computing the inner product of two variables but getting an error "inner_product was not declared in this scope" for the following code:
#include <math.h>
#include <RcppCommon.h>
#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]
using namespace Rcpp;
// [[Rcpp::export]]
NumericVector polynomial_kernel(NumericVector x, NumericMatrix Y, double scale = 1, double offset =
1, int d=1){
int n = Y.nrow();
NumericVector kernel(n);
for (int j = 0; j < n; j++){
NumericVector v = Y( j,_ );
double crossProd =innerProduct(x,v);
kernel[j]= pow((scale*crossProd+offset),2);
}
return kernel;
}
Please help me to resolve this problem.

Answer 1

Below is simpler, repaired version of your code that actually compiles. It uses Armadillo types for consistency, and instead of calling a non-existing "inner_product" routines computes the inner product of two vectors the standard way via multiplication.
#include <RcppArmadillo.h> // also pulls in Rcpp.h amd cmath
// [[Rcpp::depends(RcppArmadillo)]]
// [[Rcpp::export]]
arma::vec polynomial_kernel(arma::vec x, arma::mat Y,
double scale = 1, double offset = 1, int d=1) {
int n = Y.n_rows;
arma::vec kernel(n);
for (int j = 0; j < n; j++){
arma::rowvec v = Y.row(j);
double crossProd = arma::as_scalar(v * x);
kernel[j] = std::pow((scale*crossProd+offset),2);
}
return kernel;
}
Your example was not a minimallyc complete verifiable example so I cannot show it any data you could have supplied with. On some made up data it seems to work:
R> set.seed(123)
R> polynomial_kernel(runif(4), matrix(rnorm(16),4))
[,1]
[1,] 3.317483
[2,] 3.055690
[3,] 1.208345
[4,] 0.301834
R>