1 #ifndef STAN_MATH_FWD_SCAL_FUN_ATAN_HPP
2 #define STAN_MATH_FWD_SCAL_FUN_ATAN_HPP
3 
4 #include <stan/math/fwd/core.hpp>
5 #include <stan/math/prim/scal/fun/square.hpp>
6 #include <cmath>
7 
8 namespace stan {
9 namespace math {
10 
11 template <typename T>
atan(const fvar<T> & x)12 inline fvar<T> atan(const fvar<T>& x) {
13   using std::atan;
14   return fvar<T>(atan(x.val_), x.d_ / (1 + square(x.val_)));
15 }
16 
17 }  // namespace math
18 }  // namespace stan
19 #endif
20