fabs.hpp

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#ifndef STAN_MATH_FWD_FUN_FABS_HPP
#define STAN_MATH_FWD_FUN_FABS_HPP
 
#include <stan/math/fwd/meta.hpp>
#include <stan/math/fwd/core.hpp>
#include <stan/math/prim/fun/constants.hpp>
#include <stan/math/prim/fun/is_nan.hpp>
#include <stan/math/prim/fun/value_of.hpp>
#include <cmath>
 
namespace stan {
namespace math {
 
template <typename T>
inline fvar<T> fabs(const fvar<T>& x) {
  using std::fabs;
 
  if (unlikely(is_nan(value_of(x.val_)))) {
    return fvar<T>(fabs(x.val_), NOT_A_NUMBER);
  } else if (x.val_ > 0.0) {
    return x;
  } else if (x.val_ < 0.0) {
    return fvar<T>(-x.val_, -x.d_);
  } else {
    return fvar<T>(0, 0);
  }
}
 
}  // namespace math
}  // namespace stan
#endif