Stan Math Library  2.20.0
reverse mode automatic differentiation
inv_sqrt.hpp
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1 #ifndef STAN_MATH_FWD_SCAL_FUN_INV_SQRT_HPP
2 #define STAN_MATH_FWD_SCAL_FUN_INV_SQRT_HPP
3 
4 #include <stan/math/fwd/meta.hpp>
5 #include <stan/math/fwd/core.hpp>
6 
7 namespace stan {
8 namespace math {
9 
10 template <typename T>
11 inline fvar<T> inv_sqrt(const fvar<T>& x) {
12  using std::sqrt;
13  T sqrt_x(sqrt(x.val_));
14  return fvar<T>(1 / sqrt_x, -0.5 * x.d_ / (x.val_ * sqrt_x));
15 }
16 } // namespace math
17 } // namespace stan
18 #endif
fvar< T > inv_sqrt(const fvar< T > &x)
Definition: inv_sqrt.hpp:11
T d_
The tangent (derivative) of this variable.
Definition: fvar.hpp:50
fvar< T > sqrt(const fvar< T > &x)
Definition: sqrt.hpp:13
T val_
The value of this variable.
Definition: fvar.hpp:45
This template class represents scalars used in forward-mode automatic differentiation, which consist of values and directional derivatives of the specified template type.
Definition: fvar.hpp:41

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