Stan Math Library  2.12.0
reverse mode automatic differentiation
inv_sqrt.hpp
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1 #ifndef STAN_MATH_REV_SCAL_FUN_INV_SQRT_HPP
2 #define STAN_MATH_REV_SCAL_FUN_INV_SQRT_HPP
3 
4 #include <stan/math/rev/core.hpp>
6 #include <valarray>
7 
8 namespace stan {
9  namespace math {
10 
11  namespace {
12  class inv_sqrt_vari : public op_v_vari {
13  public:
14  explicit inv_sqrt_vari(vari* avi) :
15  op_v_vari(inv_sqrt(avi->val_), avi) {
16  }
17  void chain() {
18  avi_->adj_ -= 0.5 * adj_ / (avi_->val_ * std::sqrt(avi_->val_));
19  }
20  };
21  }
22 
42  inline var inv_sqrt(const var& a) {
43  return var(new inv_sqrt_vari(a.vi_));
44  }
45 
46  }
47 }
48 #endif
fvar< T > inv_sqrt(const fvar< T > &x)
Definition: inv_sqrt.hpp:14
fvar< T > sqrt(const fvar< T > &x)
Definition: sqrt.hpp:14
Independent (input) and dependent (output) variables for gradients.
Definition: var.hpp:30
vari * vi_
Pointer to the implementation of this variable.
Definition: var.hpp:42

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