Stan Math Library  2.9.0
reverse mode automatic differentiation
double_exponential_rng.hpp
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1 #ifndef STAN_MATH_PRIM_SCAL_PROB_DOUBLE_EXPONENTIAL_RNG_HPP
2 #define STAN_MATH_PRIM_SCAL_PROB_DOUBLE_EXPONENTIAL_RNG_HPP
3 
4 #include <boost/random/uniform_01.hpp>
5 #include <boost/random/variate_generator.hpp>
13 
17 
18 namespace stan {
19 
20  namespace math {
21 
22  template <class RNG>
23  inline double
24  double_exponential_rng(const double mu,
25  const double sigma,
26  RNG& rng) {
27  static const char* function("stan::math::double_exponential_rng");
28 
29  using boost::variate_generator;
30  using boost::random::uniform_01;
31  using std::log;
32  using std::abs;
35  using stan::math::log1m;
36 
37  check_finite(function, "Location parameter", mu);
38  check_positive_finite(function, "Scale parameter", sigma);
39 
40  variate_generator<RNG&, uniform_01<> >
41  rng_unit_01(rng, uniform_01<>());
42  double a = 0;
43  double laplaceRN = rng_unit_01();
44  if (0.5 - laplaceRN > 0)
45  a = 1.0;
46  else if (0.5 - laplaceRN < 0)
47  a = -1.0;
48  return mu - sigma * a * log1m(2 * abs(0.5 - laplaceRN));
49  }
50  }
51 }
52 #endif
fvar< T > abs(const fvar< T > &x)
Definition: abs.hpp:15
fvar< T > log(const fvar< T > &x)
Definition: log.hpp:15
bool check_finite(const char *function, const char *name, const T_y &y)
Return true if y is finite.
double double_exponential_rng(const double mu, const double sigma, RNG &rng)
bool check_positive_finite(const char *function, const char *name, const T_y &y)
Return true if y is positive and finite.
fvar< T > log1m(const fvar< T > &x)
Definition: log1m.hpp:16

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