Merge branch 'gh-pages' of github.com:jjallaire/rcpp-gallery into gh-pages

Author: jjallaire

_posts/2012-12-20-simulating-pi.md

@@ -27,7 +27,6 @@ scaling up to the full circle, we have an estimate of pi.
 
 
 
-
 {% highlight r %}
 piR <- function(N) {
     x <- runif(N)
@@ -46,7 +45,6 @@ c(piR(1000), piR(10000), piR(100000), piR(1000000))
 [1] 3.156 3.155 3.139 3.141
 </pre>
 
-
 The neat thing about Rcpp sugar enables us to write C++ code that
 looks almost as compact.  
 
@@ -56,19 +54,19 @@ using namespace Rcpp;
 
 // [[Rcpp::export]]
 double piSugar(const int N) {
-  RNGScope scope;		// ensure RNG gets set/reset
-  NumericVector x = runif(N);
-  NumericVector y = runif(N);
-  NumericVector d = sqrt(x*x + y*y);
-  return 4.0 * sum(d < 1.0) / N;
+    NumericVector x = runif(N);
+    NumericVector y = runif(N);
+    NumericVector d = sqrt(x*x + y*y);
+    return 4.0 * sum(d < 1.0) / N;
 }
 {% endhighlight %}
 
-
 Apart from using types (hey, this is C++) and assuring the RNG gets
 set and reset, the code is essentially identical.
 
-And by using the same RNG, so are the results.
+And by using the same RNG, so are the results. Rcpp ensures that
+the RNG state is set and reset properly by instantiating an object 
+of class `RNGScope`. 
 
 {% highlight r %}
 set.seed(5)
@@ -80,4 +78,3 @@ c(piSugar(1000), piSugar(10000), piSugar(100000), piSugar(1000000))
 <pre class="output">
 [1] 3.156 3.155 3.139 3.141
 </pre>
-

_posts/2012-12-22-vector-cumulative-sum.md

@@ -10,7 +10,6 @@ src: 2012-12-22-vector-cumulative-sum.cpp
 ---
 
 
-
 The traditional way to compute the cumulative sum of a vector is with a
 for loop. This is demonstrated with the function cumsum1().
 
@@ -35,7 +34,6 @@ NumericVector cumsum1(NumericVector x){
 }
 {% endhighlight %}
 
-
 The C++ standard template library (STL) has the partial_sum() function
 that computes the cumulative sum of a vector. This is demonstrated with
 the function cumsum2().
@@ -50,7 +48,6 @@ NumericVector cumsum2(NumericVector x){
  }
 {% endhighlight %}
 
-
 With Rcpp sugar, there is a cumsum() function which makes writing 
 this function in C++ very similar to using the cumsum function in R.
 
@@ -61,52 +58,15 @@ NumericVector cumsum_sug(NumericVector x){
 }
 {% endhighlight %}
 
+And we can of course compare the versions discussed here with the base R variant.
 
 {% highlight r %}
- x <- 1:10
- cumsum1(x)
-{% endhighlight %}
-
-
-
-<pre class="output">
- [1]  1  3  6 10 15 21 28 36 45 55
-</pre>
-
-
-
-{% highlight r %}
- cumsum2(x)
-{% endhighlight %}
-
-
-
-<pre class="output">
- [1]  1  3  6 10 15 21 28 36 45 55
-</pre>
-
-
-
-{% highlight r %}
- cumsum_sug(x)
+x <- 1:10
+all.equal(cumsum1(x), cumsum2(x), cumsum_sug(x), cumsum(x))
 {% endhighlight %}
 
 
 
 <pre class="output">
- [1]  1  3  6 10 15 21 28 36 45 55
+[1] TRUE
 </pre>
-
-
-
-{% highlight r %}
- # cumsum function in base R
- cumsum(x)
-{% endhighlight %}
-
-
-
-<pre class="output">
- [1]  1  3  6 10 15 21 28 36 45 55
-</pre>
-