1 #ifndef STAN_MATH_REV_FUN_LOGIT_HPP
2 #define STAN_MATH_REV_FUN_LOGIT_HPP
3 
4 #include <stan/math/rev/core.hpp>
5 #include <stan/math/rev/meta.hpp>
6 #include <stan/math/prim/fun/logit.hpp>
7 #include <stan/math/prim/fun/square.hpp>
8 
9 namespace stan {
10 namespace math {
11 
12 /**
13  * Return the log odds of the specified argument.
14  *
15  * @tparam T Arithmetic or a type inheriting from `EigenBase`.
16  * @param u The variable.
17  * @return log odds of argument
18  */
19 template <typename T, require_stan_scalar_or_eigen_t<T>* = nullptr>
logit(const var_value<T> & u)20 inline auto logit(const var_value<T>& u) {
21   auto denom = to_arena(1.0 / as_array_or_scalar(u.val() - square(u.val())));
22   return make_callback_var(logit(u.val()), [u, denom](auto& vi) mutable {
23     as_array_or_scalar(u.adj()) += as_array_or_scalar(vi.adj()) * denom;
24   });
25 }
26 
27 }  // namespace math
28 }  // namespace stan
29 #endif
30