sourceCpp.Rmd

---
title: "Using rcpptimer with Rcpp::sourceCpp"
author: Jonathan Berrisch
date: "`r Sys.Date()`"
output:
  rmarkdown::html_vignette:
    number_sections: no
    toc: no
vignette: >
  %\VignetteIndexEntry{Using rcpptimer with Rcpp::sourceCpp}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

Using `Rcpp::Timer` together with `Rcpp::sourceCpp` is similar to using it in an R package (c.f. `vignette("packages")`). However, instead of linking to rcpptimer in the `DESCRIPTION` file, we declare this dependency in the C++ file. We can do this by adding `//[[Rcpp::depends(rcpptimer)]]`. In the following, find a simple example file called 'fibonacci_omp.cpp':

```c++
// fibonacci_omp.cpp

//[[Rcpp::depends(rcpptimer)]]
#include <rcpptimer.h>

long int fib(long int n)
{
  return ((n <= 1) ? n : fib(n - 1) + fib(n - 2));
}

//[[Rcpp::export]]
std::vector<long int> fibonacci_omp(std::vector<long int> n)
{
  Rcpp::Timer timer;
  // This scoped timer measures the total execution time of 'fibonacci'
  Rcpp::Timer::ScopedTimer scpdtmr(timer, "fib_body");
  std::vector<long int> results = n;
#pragma omp parallel for
  for (unsigned int i = 0; i < n.size(); ++i)
  {
    timer.tic("fib_" + std::to_string(n[i]));
    results[i] = fib(n[i]);
    timer.toc("fib_" + std::to_string(n[i]));
  }
  return (results);
}
```

Place that file in your working directory and run:

```{r, eval = FALSE}
Rcpp::sourceCpp("fibonacci_omp.cpp")
```

This will compile the C++ code and load the function `fibonacci_omp` into your R environment. You can now call it with `fibonacci_omp(n = rep(20:25, 10))` and observe the timings by executing `print(times)`.