I encountered an error when using OptimLib library in Rcpp.First I copied sphere_fn
function online in order to use it later in optim function. However, this shere_fn
didn't work.
Error: can not initialize a member subobject of type `'arma::Col<double>*'with an lvalue of type 'SEXP'(aka'SEXPREC *').`
It seems the problem was at grad_out,but this input form is required for optim function.
For example, the optim algorithm is called using:
bool cg(arma::vec& init_out_vals, std::function<double (const arma::vec& vals_inp, arma::vec* grad_out, void* opt_data)> opt_objfn, void* opt_data);
Could anyone help me with this ?
My code is :
#include <iostream>
#include <math.h> /* sqrt */
#define USE_RCPP_ARMADILLO
#include "optim.hpp"
// [[Rcpp::depends(RcppArmadillo)]]
using namespace Rcpp;
using namespace std;
// This is a simple example of exporting a C++ function to R. You can
// source this function into an R session using the Rcpp::sourceCpp
// function (or via the Source button on the editor toolbar). Learn
// more about Rcpp at:
//
// http://www.rcpp.org/
// http://adv-r.had.co.nz/Rcpp.html
// http://gallery.rcpp.org/
//
// [[Rcpp::export]]
double sphere_fn(const arma::vec& vals_inp, arma::vec* grad_out, void* opt_data)
{
double obj_val = arma::dot(vals_inp,vals_inp);
//
if (grad_out) {
*grad_out = 2.0*vals_inp;
}
//
return obj_val;
}
Well sometime you may need to put in the time to learn to walk before you can compete in races.
In other words, you cannot just put semi-arbitrary signatures in there and expect Rcpp Attributes to translate it it all for you. What is void *
supposed to map to? Ditto for arma::vec*.
Just pass an arma::vec, it will use a pointer internally. Study some existing examples from working RcppArmadillo-using package, and maybe glance at some of the vignettes.