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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>
5 #include <stan/math/prim/scal/fun/log1m_exp.hpp>
6 #include <stan/math/rev/scal/fun/calculate_chain.hpp>
7 #include <cmath>
8
9 #ifdef _MSC_VER
10 #include <boost/math/special_functions/expm1.hpp>
11 using boost::math::expm1;
12 #endif
13
14 namespace stan {
15 namespace math {
16
17 namespace {
18 class log1m_exp_v_vari : public op_v_vari {
19 public:
20 explicit log1m_exp_v_vari(vari* avi) :
21 op_v_vari(stan::math::log1m_exp(avi->val_),
22 avi) {
23 }
24 void chain() {
25 // derivative of
26 // log(1-exp(x)) = -exp(x)/(1-exp(x))
27 // = -1/(exp(-x)-1)
28 // = -1/expm1(-x)
29 avi_->adj_ -= adj_ / ::expm1(-(avi_->val_));
30 }
31 };
32 }
33
38 inline var log1m_exp(const stan::math::var& a) {
39 return var(new log1m_exp_v_vari(a.vi_));
40 }
41
42 }
43 }
44 #endif
core.hpp
stan
Definition: log_sum_exp.hpp:8
stan::math::var
Independent (input) and dependent (output) variables for gradients.
Definition: var.hpp:31
stan::math::expm1
fvar< T > expm1(const fvar< T > &x)
Definition: expm1.hpp:12
stan::math::log1m_exp
fvar< T > log1m_exp(const fvar< T > &x)
Definition: log1m_exp.hpp:16
log1m_exp.hpp
stan::math::var::vi_
vari * vi_
Pointer to the implementation of this variable.
Definition: var.hpp:43
calculate_chain.hpp

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