Rcpp Version 0.12.12
rnchisq.h
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1 // -*- mode: C++; c-indent-level: 4; c-basic-offset: 4; indent-tabs-mode: nil; -*-
2 //
3 // rnchisq.h: Rcpp R/C++ interface class library --
4 //
5 // Copyright (C) 2010 - 2016 Douglas Bates, Dirk Eddelbuettel and Romain Francois
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21 
22 #ifndef Rcpp__stats__random_rnchisq_h
23 #define Rcpp__stats__random_rnchisq_h
24 
25 namespace Rcpp {
26 namespace stats {
27 
28 class NChisqGenerator : public ::Rcpp::Generator<double> {
29 public:
30 
31  NChisqGenerator( double df_, double lambda_ ) :
32  df(df_), df_2(df_ / 2.0), lambda_2(lambda_ / 2.0 ) {}
33 
34  inline double operator()() const {
35  double r = ::Rf_rpois( lambda_2 ) ;
36  // if( r > 0.0 ) r = Rf_rchisq( 2. * r ) ;
37  // replace by so that we can skip the tests in rchisq
38  // because there is no point in doing them as we know the
39  // outcome for sure
40  if( r > 0.0 ) r = ::Rf_rgamma( r, 2. ) ;
41  if (df > 0.) r += ::Rf_rgamma( df_2, 2.);
42  return r;
43  }
44 
45 private:
46  double df ;
47  double df_2 ;
48  double lambda_2 ;
49 };
50 
51 } // stats
52 } // Rcpp
53 
54 #endif
double operator()() const
Definition: rnchisq.h:34
NChisqGenerator(double df_, double lambda_)
Definition: rnchisq.h:31
Rcpp API.
Definition: algo.h:28