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falling_factorial.hpp
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1 #ifndef STAN_MATH_REV_SCAL_FUN_FALLING_FACTORIAL_HPP
2 #define STAN_MATH_REV_SCAL_FUN_FALLING_FACTORIAL_HPP
3 
4 #include <stan/math/rev/core.hpp>
6 #include <boost/math/special_functions/digamma.hpp>
7 
8 namespace stan {
9  namespace math {
10 
11  namespace {
12 
13  class falling_factorial_vv_vari : public op_vv_vari {
14  public:
15  falling_factorial_vv_vari(vari* avi, vari* bvi) :
16  op_vv_vari(stan::math::falling_factorial(avi->val_, bvi->val_),
17  avi, bvi) {
18  }
19  void chain() {
20  avi_->adj_ += adj_
21  * stan::math::falling_factorial(avi_->val_, bvi_->val_)
22  * boost::math::digamma(avi_->val_ + 1);
23  bvi_->adj_ -= adj_
24  * stan::math::falling_factorial(avi_->val_, bvi_->val_)
25  * boost::math::digamma(bvi_->val_ + 1);
26  }
27  };
28 
29  class falling_factorial_vd_vari : public op_vd_vari {
30  public:
31  falling_factorial_vd_vari(vari* avi, double b) :
32  op_vd_vari(stan::math::falling_factorial(avi->val_, b), avi, b) {
33  }
34  void chain() {
35  avi_->adj_ += adj_ * stan::math::falling_factorial(avi_->val_, bd_)
36  * boost::math::digamma(avi_->val_ + 1);
37  }
38  };
39 
40  class falling_factorial_dv_vari : public op_dv_vari {
41  public:
42  falling_factorial_dv_vari(double a, vari* bvi) :
43  op_dv_vari(stan::math::falling_factorial(a, bvi->val_), a, bvi) {
44  }
45  void chain() {
46  bvi_->adj_ += adj_ * -stan::math::falling_factorial(ad_, bvi_->val_)
47  * boost::math::digamma(bvi_->val_ + 1);
48  }
49  };
50  }
51 
52  inline var falling_factorial(const var& a,
53  const double& b) {
54  return var(new falling_factorial_vd_vari(a.vi_, b));
55  }
56 
57  inline var falling_factorial(const var& a,
58  const var& b) {
59  return var(new falling_factorial_vv_vari(a.vi_, b.vi_));
60  }
61 
62  inline var falling_factorial(const double& a,
63  const var& b) {
64  return var(new falling_factorial_dv_vari(a, b.vi_));
65  }
66  }
67 }
68 #endif
Independent (input) and dependent (output) variables for gradients.
Definition: var.hpp:32
vari * vi_
Pointer to the implementation of this variable.
Definition: var.hpp:44
fvar< T > falling_factorial(const fvar< T > &x, const fvar< T > &n)
fvar< T > digamma(const fvar< T > &x)
Definition: digamma.hpp:16

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