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// -*- mode: C++; c-indent-level: 4; c-basic-offset: 4; tab-width: 4 -*-
//
// rnchisq.h: Rcpp R/C++ interface class library --
//
// Copyright (C) 2010 - 2012 Douglas Bates, Dirk Eddelbuettel and Romain Francois
//
// This file is part of Rcpp.
//
// Rcpp is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 2 of the License, or
// (at your option) any later version.
//
// Rcpp is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Rcpp. If not, see <http://www.gnu.org/licenses/>.
#ifndef Rcpp__stats__random_rnchisq_h
#define Rcpp__stats__random_rnchisq_h
namespace Rcpp {
namespace stats {
class NChisqGenerator : public ::Rcpp::Generator<double> {
public:
NChisqGenerator( double df_, double lambda_ ) :
df(df_), df_2(df_ / 2.0), lambda_2(lambda_ / 2.0 ) {}
inline double operator()() const {
double r = ::Rf_rpois( lambda_2 ) ;
// if( r > 0.0 ) r = Rf_rchisq( 2. * r ) ;
// replace by so that we can skip the tests in rchisq
// because there is no point in doing them as we know the
// outcome for sure
if( r > 0.0 ) r = ::Rf_rgamma( r, 2. ) ;
if (df > 0.) r += ::Rf_rgamma( df_2, 2.);
return r;
}
private:
double df ;
double df_2 ;
double lambda_2 ;
} ;
} // stats
} // Rcpp
#endif
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