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#ifndef KOKKOS_COMPLEX_HPP
#define KOKKOS_COMPLEX_HPP

#include <Kokkos_Atomic.hpp>
#include <Kokkos_NumericTraits.hpp>
#include <complex>
#include <iostream>

namespace Kokkos {

/// \class complex
/// \brief Partial reimplementation of std::complex that works as the
///   result of a Kokkos::parallel_reduce.
/// \tparam RealType The type of the real and imaginary parts of the
///   complex number.  As with std::complex, this is only defined for
///   \c float, \c double, and <tt>long double</tt>.  The latter is
///   currently forbidden in CUDA device kernels.
template<class RealType>
class complex {
private:
  RealType re_, im_;

public:
  //! The type of the real or imaginary parts of this complex number.
  typedef RealType value_type;

  //! Default constructor (initializes both real and imaginary parts to zero).
  KOKKOS_INLINE_FUNCTION complex () :
    re_ (0.0), im_ (0.0)
  {}

  //! Copy constructor.
  KOKKOS_INLINE_FUNCTION complex (const complex<RealType>& src) :
    re_ (src.re_), im_ (src.im_)
  {}

  //! Copy constructor from volatile.
  KOKKOS_INLINE_FUNCTION complex (const volatile complex<RealType>& src) :
    re_ (src.re_), im_ (src.im_)
  {}

  /// \brief Conversion constructor from std::complex.
  ///
  /// This constructor cannot be called in a CUDA device function,
  /// because std::complex's methods and nonmember functions are not
  /// marked as CUDA device functions.
  template<class InputRealType>
  complex (const std::complex<InputRealType>& src) :
    re_ (std::real (src)), im_ (std::imag (src))
  {}

  /// \brief Conversion operator to std::complex.
  ///
  /// This operator cannot be called in a CUDA device function,
  /// because std::complex's methods and nonmember functions are not
  /// marked as CUDA device functions.
  operator std::complex<RealType> () const {
    return std::complex<RealType> (re_, im_);
  }

  /// \brief Constructor that takes just the real part, and sets the
  ///   imaginary part to zero.
  template<class InputRealType>
  KOKKOS_INLINE_FUNCTION complex (const InputRealType& val) :
    re_ (val), im_ (static_cast<InputRealType>(0.0))
  {}

  // BUG HCC WORKAROUND
  KOKKOS_INLINE_FUNCTION complex( const RealType& re, const RealType& im):
    re_ (re), im_ (im)
  {}
 
  //! Constructor that takes the real and imaginary parts.
  template<class RealType1, class RealType2>
  KOKKOS_INLINE_FUNCTION complex (const RealType1& re, const RealType2& im) :
    re_ (re), im_ (im)
  {}

  //! Assignment operator.
  template<class InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>& operator= (const complex<InputRealType>& src) {
    re_ = src.re_;
    im_ = src.im_;
    return *this;
  }

  /// \brief Assignment operator, for volatile <tt>*this</tt> and
  ///   nonvolatile input.
  ///
  /// \param src [in] Input; right-hand side of the assignment.
  ///
  /// This operator returns \c void instead of <tt>volatile
  /// complex<RealType>& </tt>.  See Kokkos Issue #177 for the
  /// explanation.  In practice, this means that you should not chain
  /// assignments with volatile lvalues.
  template<class InputRealType>
  KOKKOS_INLINE_FUNCTION
  void operator= (const complex<InputRealType>& src) volatile {
    re_ = src.re_;
    im_ = src.im_;
    // We deliberately do not return anything here.  See explanation
    // in public documentation above.
  }

  //! Assignment operator.
  template<class InputRealType>
  KOKKOS_INLINE_FUNCTION
  volatile complex<RealType>& operator= (const volatile complex<InputRealType>& src) volatile {
    re_ = src.re_;
    im_ = src.im_;
    return *this;
  }

  //! Assignment operator.
  template<class InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>& operator= (const volatile complex<InputRealType>& src) {
    re_ = src.re_;
    im_ = src.im_;
    return *this;
  }

  //! Assignment operator (from a real number).
  template<class InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>& operator= (const InputRealType& val) {
    re_ = val;
    im_ = static_cast<RealType> (0.0);
    return *this;
  }

  //! Assignment operator (from a real number).
  template<class InputRealType>
  KOKKOS_INLINE_FUNCTION
  void operator= (const InputRealType& val) volatile {
    re_ = val;
    im_ = static_cast<RealType> (0.0);
  }

  /// \brief Assignment operator from std::complex.
  ///
  /// This constructor cannot be called in a CUDA device function,
  /// because std::complex's methods and nonmember functions are not
  /// marked as CUDA device functions.
  template<class InputRealType>
  complex<RealType>& operator= (const std::complex<InputRealType>& src) {
    re_ = std::real (src);
    im_ = std::imag (src);
    return *this;
  }

  //! The imaginary part of this complex number.
  KOKKOS_INLINE_FUNCTION RealType& imag () {
    return im_;
  }

  //! The real part of this complex number.
  KOKKOS_INLINE_FUNCTION RealType& real () {
    return re_;
  }

  //! The imaginary part of this complex number.
  KOKKOS_INLINE_FUNCTION const RealType imag () const {
    return im_;
  }

  //! The real part of this complex number.
  KOKKOS_INLINE_FUNCTION const RealType real () const {
    return re_;
  }

  //! The imaginary part of this complex number (volatile overload).
  KOKKOS_INLINE_FUNCTION volatile RealType& imag () volatile {
    return im_;
  }

  //! The real part of this complex number (volatile overload).
  KOKKOS_INLINE_FUNCTION volatile RealType& real () volatile {
    return re_;
  }

  //! The imaginary part of this complex number (volatile overload).
  KOKKOS_INLINE_FUNCTION const RealType imag () const volatile {
    return im_;
  }

  //! The real part of this complex number (volatile overload).
  KOKKOS_INLINE_FUNCTION const RealType real () const volatile {
    return re_;
  }

  //! Set the imaginary part of this complex number.
  KOKKOS_INLINE_FUNCTION void imag (RealType v) {
    im_ = v;
  }

  //! Set the real part of this complex number.
  KOKKOS_INLINE_FUNCTION void real (RealType v) {
    re_ = v;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator += (const complex<InputRealType>& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    re_ += src.re_;
    im_ += src.im_;
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  void
  operator += (const volatile complex<InputRealType>& src) volatile {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    re_ += src.re_;
    im_ += src.im_;
  }

  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator += (const std::complex<RealType>& src) {
    re_ += src.real();
    im_ += src.imag();
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator += (const InputRealType& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    re_ += src;
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  void
  operator += (const volatile InputRealType& src) volatile {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    re_ += src;
  }
  
  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator -= (const complex<InputRealType>& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    re_ -= src.re_;
    im_ -= src.im_;
    return *this;
  }

  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator -= (const std::complex<RealType>& src) {
    re_ -= src.real();
    im_ -= src.imag();
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator -= (const InputRealType& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    re_ -= src;
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator *= (const complex<InputRealType>& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    const RealType realPart = re_ * src.re_ - im_ * src.im_;
    const RealType imagPart = re_ * src.im_ + im_ * src.re_;
    re_ = realPart;
    im_ = imagPart;
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  void
  operator *= (const volatile complex<InputRealType>& src) volatile {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    const RealType realPart = re_ * src.re_ - im_ * src.im_;
    const RealType imagPart = re_ * src.im_ + im_ * src.re_;
    re_ = realPart;
    im_ = imagPart;
  }

  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator *= (const std::complex<RealType>& src) {
    const RealType realPart = re_ * src.real() - im_ * src.imag();
    const RealType imagPart = re_ * src.imag() + im_ * src.real();
    re_ = realPart;
    im_ = imagPart;
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator *= (const InputRealType& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    re_ *= src;
    im_ *= src;
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  void
  operator *= (const volatile InputRealType& src) volatile {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");
    re_ *= src;
    im_ *= src;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator /= (const complex<InputRealType>& y) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");

    // Scale (by the "1-norm" of y) to avoid unwarranted overflow.
    // If the real part is +/-Inf and the imaginary part is -/+Inf,
    // this won't change the result.
    const RealType s = std::fabs (y.real ()) + std::fabs (y.imag ());

    // If s is 0, then y is zero, so x/y == real(x)/0 + i*imag(x)/0.
    // In that case, the relation x/y == (x/s) / (y/s) doesn't hold,
    // because y/s is NaN.
    if (s == 0.0) {
      this->re_ /= s;
      this->im_ /= s;
    }
    else {
      const complex<RealType> x_scaled (this->re_ / s, this->im_ / s);
      const complex<RealType> y_conj_scaled (y.re_ / s, -(y.im_) / s);
      const RealType y_scaled_abs = y_conj_scaled.re_ * y_conj_scaled.re_ +
        y_conj_scaled.im_ * y_conj_scaled.im_; // abs(y) == abs(conj(y))
      *this = x_scaled * y_conj_scaled;
      *this /= y_scaled_abs;
    }
    return *this;
  }
  
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator /= (const std::complex<RealType>& y) {

    // Scale (by the "1-norm" of y) to avoid unwarranted overflow.
    // If the real part is +/-Inf and the imaginary part is -/+Inf,
    // this won't change the result.
    const RealType s = std::fabs (y.real ()) + std::fabs (y.imag ());

    // If s is 0, then y is zero, so x/y == real(x)/0 + i*imag(x)/0.
    // In that case, the relation x/y == (x/s) / (y/s) doesn't hold,
    // because y/s is NaN.
    if (s == 0.0) {
      this->re_ /= s;
      this->im_ /= s;
    }
    else {
      const complex<RealType> x_scaled (this->re_ / s, this->im_ / s);
      const complex<RealType> y_conj_scaled (y.re_ / s, -(y.im_) / s);
      const RealType y_scaled_abs = y_conj_scaled.re_ * y_conj_scaled.re_ +
        y_conj_scaled.im_ * y_conj_scaled.im_; // abs(y) == abs(conj(y))
      *this = x_scaled * y_conj_scaled;
      *this /= y_scaled_abs;
    }
    return *this;
  }


  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  complex<RealType>&
  operator /= (const InputRealType& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");

    re_ /= src;
    im_ /= src;
    return *this;
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  bool
  operator == (const complex<InputRealType>& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");

    return (re_ == static_cast<RealType>(src.re_)) && (im_ == static_cast<RealType>(src.im_));
  }

  KOKKOS_INLINE_FUNCTION
  bool
  operator == (const std::complex<RealType>& src) {
    return (re_ == src.real()) && (im_ == src.imag());
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  bool
  operator == (const InputRealType src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");

    return (re_ == static_cast<RealType>(src)) && (im_ == RealType(0));
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  bool
  operator != (const complex<InputRealType>& src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");

    return (re_ != static_cast<RealType>(src.re_)) || (im_ != static_cast<RealType>(src.im_));
  }

  KOKKOS_INLINE_FUNCTION
  bool
  operator != (const std::complex<RealType>& src) {
    return (re_ != src.real()) || (im_ != src.imag());
  }

  template<typename InputRealType>
  KOKKOS_INLINE_FUNCTION
  bool
  operator != (const InputRealType src) {
    static_assert(std::is_convertible<InputRealType,RealType>::value, 
                  "InputRealType must be convertible to RealType");

    return (re_ != static_cast<RealType>(src)) || (im_ != RealType(0));
  }
  
};


//! Binary + operator for complex complex.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator + (const complex<RealType1>& x, const complex<RealType2>& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type > (x.real () + y.real (), x.imag () + y.imag ());
}

//! Binary + operator for complex scalar.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator + (const complex<RealType1>& x, const RealType2& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x.real () + y , x.imag ());
}

//! Binary + operator for scalar complex.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator + (const RealType1& x, const complex<RealType2>& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x + y.real (), y.imag ());
}

//! Unary + operator for complex.
template<class RealType>
KOKKOS_INLINE_FUNCTION
complex<RealType>
operator + (const complex<RealType>& x) {
  return x;
}

//! Binary - operator for complex.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator - (const complex<RealType1>& x, const complex<RealType2>& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x.real () - y.real (), x.imag () - y.imag ());
}

//! Binary - operator for complex scalar.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator - (const complex<RealType1>& x, const RealType2& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x.real () - y , x.imag ());
}

//! Binary - operator for scalar complex.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator - (const RealType1& x, const complex<RealType2>& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x - y.real (), - y.imag ());
}

//! Unary - operator for complex.
template<class RealType>
KOKKOS_INLINE_FUNCTION
complex<RealType>
operator - (const complex<RealType>& x) {
  return complex<RealType> (-x.real (), -x.imag ());
}

//! Binary * operator for complex.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator * (const complex<RealType1>& x, const complex<RealType2>& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x.real () * y.real () - x.imag () * y.imag (),
                                                                        x.real () * y.imag () + x.imag () * y.real ());
}

/// \brief Binary * operator for std::complex and complex.
///
/// This function exists because GCC 4.7.2 (and perhaps other
/// compilers) are not able to deduce that they can multiply
/// std::complex by Kokkos::complex, by first converting std::complex
/// to Kokkos::complex.
///
/// This function cannot be called in a CUDA device function, because
/// std::complex's methods and nonmember functions are not marked as
/// CUDA device functions.
template<class RealType1, class RealType2>
inline
complex<typename std::common_type<RealType1,RealType2>::type>
operator * (const std::complex<RealType1>& x, const complex<RealType2>& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x.real () * y.real () - x.imag () * y.imag (),
                                                                        x.real () * y.imag () + x.imag () * y.real ());
}

/// \brief Binary * operator for RealType times complex.
///
/// This function exists because the compiler doesn't know that
/// RealType and complex<RealType> commute with respect to operator*.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator * (const RealType1& x, const complex<RealType2>& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x * y.real (), x * y.imag ());
}

/// \brief Binary * operator for RealType times complex.
///
/// This function exists because the compiler doesn't know that
/// RealType and complex<RealType> commute with respect to operator*.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator * (const complex<RealType1>& y, const RealType2& x) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x * y.real (), x * y.imag ());
}

//! Imaginary part of a complex number.
template<class RealType>
KOKKOS_INLINE_FUNCTION
RealType imag (const complex<RealType>& x) {
  return x.imag ();
}

//! Real part of a complex number.
template<class RealType>
KOKKOS_INLINE_FUNCTION
RealType real (const complex<RealType>& x) {
  return x.real ();
}

//! Absolute value (magnitude) of a complex number.
template<class RealType>
KOKKOS_INLINE_FUNCTION
RealType abs (const complex<RealType>& x) {
  // FIXME (mfh 31 Oct 2014) Scale to avoid unwarranted overflow.
  return std::sqrt (real (x) * real (x) + imag (x) * imag (x));
}

//! Power of a complex number
template<class RealType>
KOKKOS_INLINE_FUNCTION
Kokkos::complex<RealType> pow (const complex<RealType>& x, const RealType& e) {
  RealType r = abs(x);
  RealType phi = std::atan(x.imag()/x.real());
  return std::pow(r,e) * Kokkos::complex<RealType>(std::cos(phi*e),std::sin(phi*e)); 
}

//! Square root of a complex number.
template<class RealType>
KOKKOS_INLINE_FUNCTION
Kokkos::complex<RealType> sqrt (const complex<RealType>& x) {
  RealType r = abs(x);
  RealType phi = std::atan(x.imag()/x.real());
  return std::sqrt(r) * Kokkos::complex<RealType>(std::cos(phi*0.5),std::sin(phi*0.5));
}

//! Conjugate of a complex number.
template<class RealType>
KOKKOS_INLINE_FUNCTION
complex<RealType> conj (const complex<RealType>& x) {
  return complex<RealType> (real (x), -imag (x));
}

//! Exponential of a complex number.
template<class RealType>
KOKKOS_INLINE_FUNCTION
complex<RealType> exp (const complex<RealType>& x) {
  return std::exp(x.real()) * complex<RealType> (std::cos (x.imag()),  std::sin(x.imag()));
}

/// This function cannot be called in a CUDA device function,
/// because std::complex's methods and nonmember functions are not
/// marked as CUDA device functions.
template<class RealType>
inline
complex<RealType>
exp (const std::complex<RealType>& c) {
  return complex<RealType>( std::exp( c.real() )*std::cos( c.imag() ), std::exp( c.real() )*std::sin( c.imag() ) );
}

//! Binary operator / for complex and real numbers
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator / (const complex<RealType1>& x, const RealType2& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (real (x) / y, imag (x) / y);
}

//! Binary operator / for complex.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator / (const complex<RealType1>& x, const complex<RealType2>& y) {
  // Scale (by the "1-norm" of y) to avoid unwarranted overflow.
  // If the real part is +/-Inf and the imaginary part is -/+Inf,
  // this won't change the result.
  typedef typename std::common_type<RealType1,RealType2>::type common_real_type;
  const common_real_type s = std::fabs (real (y)) + std::fabs (imag (y));

  // If s is 0, then y is zero, so x/y == real(x)/0 + i*imag(x)/0.
  // In that case, the relation x/y == (x/s) / (y/s) doesn't hold,
  // because y/s is NaN.
  if (s == 0.0) {
    return complex<common_real_type> (real (x) / s, imag (x) / s);
  }
  else {
    const complex<common_real_type> x_scaled (real (x) / s, imag (x) / s);
    const complex<common_real_type> y_conj_scaled (real (y) / s, -imag (y) / s);
    const RealType1 y_scaled_abs = real (y_conj_scaled) * real (y_conj_scaled) +
      imag (y_conj_scaled) * imag (y_conj_scaled); // abs(y) == abs(conj(y))
    complex<common_real_type> result = x_scaled * y_conj_scaled;
    result /= y_scaled_abs;
    return result;
  }
}

//! Binary operator / for complex and real numbers
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
complex<typename std::common_type<RealType1,RealType2>::type>
operator / (const RealType1& x, const complex<RealType2>& y) {
  return complex<typename std::common_type<RealType1,RealType2>::type> (x)/y;
}

//! Equality operator for two complex numbers.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
bool
operator == (const complex<RealType1>& x, const complex<RealType2>& y) {
  typedef typename std::common_type<RealType1,RealType2>::type common_real_type;
  return ( static_cast<common_real_type>(real (x)) == static_cast<common_real_type>(real (y)) && 
           static_cast<common_real_type>(imag (x)) == static_cast<common_real_type>(imag (y)) );
}

/// \brief Equality operator for std::complex and Kokkos::complex.
///
/// This cannot be a device function, since std::real is not.
/// Otherwise, CUDA builds will give compiler warnings ("warning:
/// calling a constexpr __host__ function("real") from a __host__
/// __device__ function("operator==") is not allowed").
template<class RealType1, class RealType2>
inline
bool
operator == (const std::complex<RealType1>& x, const complex<RealType2>& y) {
  typedef typename std::common_type<RealType1,RealType2>::type common_real_type;
  return ( static_cast<common_real_type>(std::real (x)) == static_cast<common_real_type>(real (y)) && 
           static_cast<common_real_type>(std::imag (x)) == static_cast<common_real_type>(imag (y)) );
}
  
//! Equality operator for complex and real number.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
bool
operator == (const complex<RealType1>& x, const RealType2& y) {
  typedef typename std::common_type<RealType1,RealType2>::type common_real_type;
  return ( static_cast<common_real_type>(real (x)) == static_cast<common_real_type>(y) && 
           static_cast<common_real_type>(imag (x)) == static_cast<common_real_type>(0.0) );
}

//! Equality operator for real and complex number.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
bool
operator == (const RealType1& x, const complex<RealType2>& y) {
  return y == x;
}

//! Inequality operator for two complex numbers.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
bool
operator != (const complex<RealType1>& x, const complex<RealType2>& y) {
  typedef typename std::common_type<RealType1,RealType2>::type common_real_type;
  return ( static_cast<common_real_type>(real (x)) != static_cast<common_real_type>(real (y)) || 
           static_cast<common_real_type>(imag (x)) != static_cast<common_real_type>(imag (y)) );
}

//! Inequality operator for std::complex and Kokkos::complex.
template<class RealType1, class RealType2>
inline
bool
operator != (const std::complex<RealType1>& x, const complex<RealType2>& y) {
  typedef typename std::common_type<RealType1,RealType2>::type common_real_type;
  return ( static_cast<common_real_type>(std::real (x)) != static_cast<common_real_type>(real (y)) || 
           static_cast<common_real_type>(std::imag (x)) != static_cast<common_real_type>(imag (y)) );
}

//! Inequality operator for complex and real number.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
bool
operator != (const complex<RealType1>& x, const RealType2& y) {
  typedef typename std::common_type<RealType1,RealType2>::type common_real_type;
  return ( static_cast<common_real_type>(real (x)) != static_cast<common_real_type>(y) || 
           static_cast<common_real_type>(imag (x)) != static_cast<common_real_type>(0.0) );
}

//! Inequality operator for real and complex number.
template<class RealType1, class RealType2>
KOKKOS_INLINE_FUNCTION
bool
operator != (const RealType1& x, const complex<RealType2>& y) {
  return y != x;
}

template<class RealType>
std::ostream& operator << (std::ostream& os, const complex<RealType>& x) {
  const std::complex<RealType> x_std (Kokkos::real (x), Kokkos::imag (x));
  os << x_std;
  return os;
}

template<class RealType>
std::ostream& operator >> (std::ostream& os, complex<RealType>& x) {
  std::complex<RealType> x_std;
  os >> x_std;
  x = x_std; // only assigns on success of above
  return os;
}


template<class T>
struct reduction_identity<Kokkos::complex<T> > {
  typedef reduction_identity<T> t_red_ident;
  KOKKOS_FORCEINLINE_FUNCTION constexpr static Kokkos::complex<T> sum()
      {return Kokkos::complex<T>(t_red_ident::sum(),t_red_ident::sum());}
  KOKKOS_FORCEINLINE_FUNCTION constexpr static Kokkos::complex<T> prod()
      {return Kokkos::complex<T>(t_red_ident::prod(),t_red_ident::sum());}
};

} // namespace Kokkos

#endif // KOKKOS_COMPLEX_HPP
