1 #ifndef STAN_MATH_REV_FUN_LOG1M_EXP_HPP 2 #define STAN_MATH_REV_FUN_LOG1M_EXP_HPP 3 4 #include <stan/math/rev/meta.hpp> 5 #include <stan/math/rev/core.hpp> 6 #include <stan/math/prim/fun/expm1.hpp> 7 #include <stan/math/prim/fun/log1m_exp.hpp> 8 9 namespace stan { 10 namespace math { 11 12 /** 13 * Return the log of 1 minus the exponential of the specified 14 * variable. 15 * 16 * <p>The derivative of <code>log(1 - exp(x))</code> with respect 17 * to <code>x</code> is <code>-1 / expm1(-x)</code>. 18 * 19 * @tparam T Arithmetic or a type inheriting from `EigenBase`. 20 * @param[in] x Argument. 21 * @return Natural logarithm of one minus the exponential of the 22 * argument. 23 */ 24 template <typename T, require_stan_scalar_or_eigen_t<T>* = nullptr> log1m_exp(const var_value<T> & x)25inline auto log1m_exp(const var_value<T>& x) { 26 return make_callback_var(log1m_exp(x.val()), [x](auto& vi) mutable { 27 as_array_or_scalar(x.adj()) 28 -= as_array_or_scalar(vi.adj()) / as_array_or_scalar(expm1(-x.val())); 29 }); 30 } 31 32 } // namespace math 33 } // namespace stan 34 #endif 35