1 #ifndef STAN_MATH_FWD_SCAL_FUN_ABS_HPP
2 #define STAN_MATH_FWD_SCAL_FUN_ABS_HPP
3 
4 #include <stan/math/fwd/core.hpp>
5 #include <stan/math/fwd/scal/fun/value_of.hpp>
6 #include <stan/math/prim/scal/fun/constants.hpp>
7 #include <stan/math/prim/scal/fun/abs.hpp>
8 #include <stan/math/prim/scal/fun/value_of.hpp>
9 #include <stan/math/prim/scal/meta/likely.hpp>
10 
11 namespace stan {
12 namespace math {
13 
14 template <typename T>
abs(const fvar<T> & x)15 inline fvar<T> abs(const fvar<T>& x) {
16   if (x.val_ > 0.0)
17     return x;
18   else if (x.val_ < 0.0)
19     return fvar<T>(-x.val_, -x.d_);
20   else if (x.val_ == 0.0)
21     return fvar<T>(0, 0);
22   else
23     return fvar<T>(abs(x.val_), NOT_A_NUMBER);
24 }
25 
26 }  // namespace math
27 }  // namespace stan
28 #endif
29