Stan Math Library  2.9.0
reverse mode automatic differentiation
operator_division.hpp
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1 #ifndef STAN_MATH_REV_CORE_OPERATOR_DIVISION_HPP
2 #define STAN_MATH_REV_CORE_OPERATOR_DIVISION_HPP
3 
8 #include <boost/math/special_functions/fpclassify.hpp>
9 #include <limits>
10 
11 namespace stan {
12  namespace math {
13 
14  namespace {
15  // (a/b)' = a' * (1 / b) - b' * (a / [b * b])
16  class divide_vv_vari : public op_vv_vari {
17  public:
18  divide_vv_vari(vari* avi, vari* bvi) :
19  op_vv_vari(avi->val_ / bvi->val_, avi, bvi) {
20  }
21  void chain() {
22  if (unlikely(boost::math::isnan(avi_->val_)
23  || boost::math::isnan(bvi_->val_))) {
24  avi_->adj_ = std::numeric_limits<double>::quiet_NaN();
25  bvi_->adj_ = std::numeric_limits<double>::quiet_NaN();
26  } else {
27  avi_->adj_ += adj_ / bvi_->val_;
28  bvi_->adj_ -= adj_ * avi_->val_ / (bvi_->val_ * bvi_->val_);
29  }
30  }
31  };
32 
33  class divide_vd_vari : public op_vd_vari {
34  public:
35  divide_vd_vari(vari* avi, double b) :
36  op_vd_vari(avi->val_ / b, avi, b) {
37  }
38  void chain() {
39  if (unlikely(boost::math::isnan(avi_->val_)
40  || boost::math::isnan(bd_)))
41  avi_->adj_ = std::numeric_limits<double>::quiet_NaN();
42  else
43  avi_->adj_ += adj_ / bd_;
44  }
45  };
46 
47  class divide_dv_vari : public op_dv_vari {
48  public:
49  divide_dv_vari(double a, vari* bvi) :
50  op_dv_vari(a / bvi->val_, a, bvi) {
51  }
52  void chain() {
53  bvi_->adj_ -= adj_ * ad_ / (bvi_->val_ * bvi_->val_);
54  }
55  };
56  }
57 
96  inline var operator/(const var& a, const var& b) {
97  return var(new divide_vv_vari(a.vi_, b.vi_));
98  }
99 
111  inline var operator/(const var& a, const double b) {
112  if (b == 1.0)
113  return a;
114  return var(new divide_vd_vari(a.vi_, b));
115  }
116 
128  inline var operator/(const double a, const var& b) {
129  return var(new divide_dv_vari(a, b.vi_));
130  }
131 
132  }
133 }
134 #endif
fvar< T > operator/(const fvar< T > &x1, const fvar< T > &x2)
Independent (input) and dependent (output) variables for gradients.
Definition: var.hpp:31
bool isnan(const stan::math::var &v)
Checks if the given number is NaN.
Definition: boost_isnan.hpp:22
#define unlikely(x)
Definition: likely.hpp:9
vari * vi_
Pointer to the implementation of this variable.
Definition: var.hpp:43

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