Stan Math Library  2.14.0
reverse mode automatic differentiation
fdim.hpp
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1 #ifndef STAN_MATH_REV_SCAL_FUN_FDIM_HPP
2 #define STAN_MATH_REV_SCAL_FUN_FDIM_HPP
3 
6 #include <stan/math/rev/core.hpp>
7 #include <limits>
8 
9 namespace stan {
10  namespace math {
11 
12  namespace {
13  class fdim_vv_vari : public op_vv_vari {
14  public:
15  fdim_vv_vari(vari* avi, vari* bvi) :
16  op_vv_vari(avi->val_ - bvi->val_, avi, bvi) {
17  }
18  void chain() {
19  if (unlikely(is_nan(avi_->val_) || is_nan(bvi_->val_))) {
20  avi_->adj_ = std::numeric_limits<double>::quiet_NaN();
21  bvi_->adj_ = std::numeric_limits<double>::quiet_NaN();
22  } else {
23  avi_->adj_ += adj_;
24  bvi_->adj_ -= adj_;
25  }
26  }
27  };
28 
29  class fdim_vd_vari : public op_vd_vari {
30  public:
31  fdim_vd_vari(vari* avi, double b) :
32  op_vd_vari(avi->val_ - b, avi, b) {
33  }
34  void chain() {
35  if (unlikely(is_nan(avi_->val_) || is_nan(bd_)))
36  avi_->adj_ = std::numeric_limits<double>::quiet_NaN();
37  else
38  avi_->adj_ += adj_;
39  }
40  };
41 
42  class fdim_dv_vari : public op_dv_vari {
43  public:
44  fdim_dv_vari(double a, vari* bvi) :
45  op_dv_vari(a - bvi->val_, a, bvi) {
46  }
47  void chain() {
48  if (unlikely(is_nan(bvi_->val_) || is_nan(ad_)))
49  bvi_->adj_ = std::numeric_limits<double>::quiet_NaN();
50  else
51  bvi_->adj_ -= adj_;
52  }
53  };
54  }
55 
94  inline var fdim(const var& a, const var& b) {
95  // reversed test to get NaN vals automatically in second case
96  return (a.vi_->val_ <= b.vi_->val_)
97  ? var(new vari(0.0))
98  : var(new fdim_vv_vari(a.vi_, b.vi_));
99  }
100 
113  inline var fdim(double a, const var& b) {
114  // reversed test to get NaN vals automatically in second case
115  return a <= b.vi_->val_
116  ? var(new vari(0.0))
117  : var(new fdim_dv_vari(a, b.vi_));
118  }
119 
131  inline var fdim(const var& a, double b) {
132  // reversed test to get NaN vals automatically in second case
133  return a.vi_->val_ <= b
134  ? var(new vari(0.0))
135  : var(new fdim_vd_vari(a.vi_, b));
136  }
137 
138  }
139 }
140 #endif
The variable implementation base class.
Definition: vari.hpp:30
Independent (input) and dependent (output) variables for gradients.
Definition: var.hpp:30
const double val_
The value of this variable.
Definition: vari.hpp:38
fvar< T > fdim(const fvar< T > &x, const fvar< T > &y)
Return the positive difference of the specified values (C++11).
Definition: fdim.hpp:20
#define unlikely(x)
Definition: likely.hpp:9
vari * vi_
Pointer to the implementation of this variable.
Definition: var.hpp:42
int is_nan(const fvar< T > &x)
Returns 1 if the input&#39;s value is NaN and 0 otherwise.
Definition: is_nan.hpp:21

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