text: #ifndef STAN_MATH_FWD_FUN_TANH_HPP
  #define STAN_MATH_FWD_FUN_TANH_HPP
  
  #include <stan/math/fwd/meta.hpp>
  #include <stan/math/fwd/core.hpp>
  #include <cmath>
  
  namespace stan {
  namespace math {
  
  template <typename T>
  inline fvar<T> tanh(const fvar<T>& x) {
    using std::tanh;
    T u = tanh(x.val_);
    return fvar<T>(u, x.d_ * (1 - u * u));
  }
  }  // namespace math
  }  // namespace stan
  #endif
  