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log1m_exp.hpp
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1 #ifndef STAN_MATH_REV_SCAL_FUN_LOG1M_EXP_HPP
2 #define STAN_MATH_REV_SCAL_FUN_LOG1M_EXP_HPP
3 
4 #include <stan/math/rev/core.hpp>
7 #include <cmath>
8 
9 namespace stan {
10  namespace math {
11 
12  namespace {
13  class log1m_exp_v_vari : public op_v_vari {
14  public:
15  explicit log1m_exp_v_vari(vari* avi) :
16  op_v_vari(stan::math::log1m_exp(avi->val_),
17  avi) {
18  }
19  void chain() {
20  // derivative of
21  // log(1-exp(x)) = -exp(x)/(1-exp(x))
22  // = -1/(exp(-x)-1)
23  // = -1/expm1(-x)
24  avi_->adj_ -= adj_ / ::expm1(-(avi_->val_));
25  }
26  };
27  }
28 
33  inline var log1m_exp(const stan::math::var& a) {
34  return var(new log1m_exp_v_vari(a.vi_));
35  }
36 
37  }
38 }
39 #endif
Independent (input) and dependent (output) variables for gradients.
Definition: var.hpp:32
fvar< T > expm1(const fvar< T > &x)
Definition: expm1.hpp:12
fvar< T > log1m_exp(const fvar< T > &x)
Definition: log1m_exp.hpp:16
vari * vi_
Pointer to the implementation of this variable.
Definition: var.hpp:44

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