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log_falling_factorial.hpp
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1 #ifndef STAN_MATH_FWD_SCAL_FUN_LOG_FALLING_FACTORIAL_HPP
2 #define STAN_MATH_FWD_SCAL_FUN_LOG_FALLING_FACTORIAL_HPP
3
4 #include <stan/math/fwd/core.hpp>
5
6 #include <stan/math/prim/scal/fun/log_falling_factorial.hpp>
7 #include <boost/math/special_functions/digamma.hpp>
8
9 namespace stan {
10 namespace math {
11
12 template<typename T>
13 inline fvar<T>
14 log_falling_factorial(const fvar<T>& x, const fvar<T>& n) {
15 using boost::math::digamma;
16
17 return fvar<T>(log_falling_factorial(x.val_, n.val_),
18 (digamma(x.val_ + 1)
19 - digamma(x.val_ - n.val_ + 1)) * x.d_
20 + digamma(x.val_ - n.val_ + 1) * n.d_);
21 }
22
23 template<typename T>
24 inline fvar<T>
25 log_falling_factorial(const double x, const fvar<T>& n) {
26 using boost::math::digamma;
27
28 return fvar<T>(log_falling_factorial(x, n.val_),
29 digamma(x - n.val_ + 1) * n.d_);
30 }
31
32 template<typename T>
33 inline fvar<T>
34 log_falling_factorial(const fvar<T>& x, const double n) {
35 using boost::math::digamma;
36
37 return fvar<T>(log_falling_factorial(x.val_, n),
38 (digamma(x.val_ + 1)
39 - digamma(x.val_ - n + 1)) * x.d_);
40 }
41 }
42 }
43 #endif
core.hpp
stan::math::log_falling_factorial
fvar< T > log_falling_factorial(const fvar< T > &x, const fvar< T > &n)
Definition: log_falling_factorial.hpp:14
stan::math::fvar::d_
T d_
Definition: fvar.hpp:14
stan
Definition: log_sum_exp.hpp:8
stan::math::fvar::val_
T val_
Definition: fvar.hpp:13
log_falling_factorial.hpp
stan::math::fvar
Definition: fvar.hpp:12
stan::math::digamma
fvar< T > digamma(const fvar< T > &x)
Definition: digamma.hpp:15

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