Data/Complex.hs

    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE StandaloneDeriving #-}
    {-# LANGUAGE DeriveGeneric #-}
    {-# LANGUAGE DeriveTraversable #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Complex
    -- Copyright   :  (c) The University of Glasgow 2001
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  provisional
    -- Portability :  portable
    --
    -- Complex numbers.
    --
    -----------------------------------------------------------------------------

    module Data.Complex
            (
            -- * Rectangular form
              Complex((:+))

            , realPart
            , imagPart
            -- * Polar form
            , mkPolar
            , cis
            , polar
            , magnitude
            , phase
            -- * Conjugate
            , conjugate

            )  where

    import GHC.Generics (Generic, Generic1)
    import GHC.Float (Floating(..))
    import Data.Data (Data)
    import Foreign (Storable, castPtr, peek, poke, pokeElemOff, peekElemOff, sizeOf,
                    alignment)

    infix  6  :+

    -- -----------------------------------------------------------------------------
    -- The Complex type

    -- | Complex numbers are an algebraic type.
    --
    -- For a complex number @z@, @'abs' z@ is a number with the magnitude of @z@,
    -- but oriented in the positive real direction, whereas @'signum' z@
    -- has the phase of @z@, but unit magnitude.
    --
    -- The 'Foldable' and 'Traversable' instances traverse the real part first.
    data Complex a
      = !a :+ !a    -- ^ forms a complex number from its real and imaginary
                    -- rectangular components.
            deriving (Eq, Show, Read, Data, Generic, Generic1
                    , Functor, Foldable, Traversable)

    -- -----------------------------------------------------------------------------
    -- Functions over Complex

    -- | Extracts the real part of a complex number.
    realPart :: Complex a -> a
    realPart (x :+ _) =  x

    -- | Extracts the imaginary part of a complex number.
    imagPart :: Complex a -> a
    imagPart (_ :+ y) =  y

    -- | The conjugate of a complex number.
    {-# SPECIALISE conjugate :: Complex Double -> Complex Double #-}
    conjugate        :: Num a => Complex a -> Complex a
    conjugate (x:+y) =  x :+ (-y)

    -- | Form a complex number from polar components of magnitude and phase.
    {-# SPECIALISE mkPolar :: Double -> Double -> Complex Double #-}
    mkPolar          :: Floating a => a -> a -> Complex a
    mkPolar r theta  =  r * cos theta :+ r * sin theta

    -- | @'cis' t@ is a complex value with magnitude @1@
    -- and phase @t@ (modulo @2*'pi'@).
    {-# SPECIALISE cis :: Double -> Complex Double #-}
    cis              :: Floating a => a -> Complex a
    cis theta        =  cos theta :+ sin theta

    -- | The function 'polar' takes a complex number and
    -- returns a (magnitude, phase) pair in canonical form:
    -- the magnitude is nonnegative, and the phase in the range @(-'pi', 'pi']@;
    -- if the magnitude is zero, then so is the phase.
    {-# SPECIALISE polar :: Complex Double -> (Double,Double) #-}
    polar            :: (RealFloat a) => Complex a -> (a,a)
    polar z          =  (magnitude z, phase z)

    -- | The nonnegative magnitude of a complex number.
    {-# SPECIALISE magnitude :: Complex Double -> Double #-}
    magnitude :: (RealFloat a) => Complex a -> a
    magnitude (x:+y) =  scaleFloat k
                         (sqrt (sqr (scaleFloat mk x) + sqr (scaleFloat mk y)))
                        where k  = max (exponent x) (exponent y)
                              mk = - k
                              sqr z = z * z

    -- | The phase of a complex number, in the range @(-'pi', 'pi']@.
    -- If the magnitude is zero, then so is the phase.
    {-# SPECIALISE phase :: Complex Double -> Double #-}
    phase :: (RealFloat a) => Complex a -> a
    phase (0 :+ 0)   = 0            -- SLPJ July 97 from John Peterson
    phase (x:+y)     = atan2 y x

    -- -----------------------------------------------------------------------------
    -- Instances of Complex

    instance  (RealFloat a) => Num (Complex a)  where
        {-# SPECIALISE instance Num (Complex Float) #-}
        {-# SPECIALISE instance Num (Complex Double) #-}
        (x:+y) + (x':+y')   =  (x+x') :+ (y+y')
        (x:+y) - (x':+y')   =  (x-x') :+ (y-y')
        (x:+y) * (x':+y')   =  (x*x'-y*y') :+ (x*y'+y*x')
        negate (x:+y)       =  negate x :+ negate y
        abs z               =  magnitude z :+ 0
        signum (0:+0)       =  0
        signum z@(x:+y)     =  x/r :+ y/r  where r = magnitude z
        fromInteger n       =  fromInteger n :+ 0

    instance  (RealFloat a) => Fractional (Complex a)  where
        {-# SPECIALISE instance Fractional (Complex Float) #-}
        {-# SPECIALISE instance Fractional (Complex Double) #-}
        (x:+y) / (x':+y')   =  (x*x''+y*y'') / d :+ (y*x''-x*y'') / d
                               where x'' = scaleFloat k x'
                                     y'' = scaleFloat k y'
                                     k   = - max (exponent x') (exponent y')
                                     d   = x'*x'' + y'*y''

        fromRational a      =  fromRational a :+ 0

    instance  (RealFloat a) => Floating (Complex a) where
        {-# SPECIALISE instance Floating (Complex Float) #-}
        {-# SPECIALISE instance Floating (Complex Double) #-}
        pi             =  pi :+ 0
        exp (x:+y)     =  expx * cos y :+ expx * sin y
                          where expx = exp x
        log z          =  log (magnitude z) :+ phase z

        x ** y = case (x,y) of
          (_ , (0:+0))  -> 1 :+ 0
          ((0:+0), (exp_re:+_)) -> case compare exp_re 0 of
                     GT -> 0 :+ 0
                     LT -> inf :+ 0
                     EQ -> nan :+ nan
          ((re:+im), (exp_re:+_))
            | (isInfinite re || isInfinite im) -> case compare exp_re 0 of
                     GT -> inf :+ 0
                     LT -> 0 :+ 0
                     EQ -> nan :+ nan
            | otherwise -> exp (log x * y)
          where
            inf = 1/0
            nan = 0/0

        sqrt (0:+0)    =  0
        sqrt z@(x:+y)  =  u :+ (if y < 0 then -v else v)
                          where (u,v) = if x < 0 then (v',u') else (u',v')
                                v'    = abs y / (u'*2)
                                u'    = sqrt ((magnitude z + abs x) / 2)

        sin (x:+y)     =  sin x * cosh y :+ cos x * sinh y
        cos (x:+y)     =  cos x * cosh y :+ (- sin x * sinh y)
        tan (x:+y)     =  (sinx*coshy:+cosx*sinhy)/(cosx*coshy:+(-sinx*sinhy))
                          where sinx  = sin x
                                cosx  = cos x
                                sinhy = sinh y
                                coshy = cosh y

        sinh (x:+y)    =  cos y * sinh x :+ sin  y * cosh x
        cosh (x:+y)    =  cos y * cosh x :+ sin y * sinh x
        tanh (x:+y)    =  (cosy*sinhx:+siny*coshx)/(cosy*coshx:+siny*sinhx)
                          where siny  = sin y
                                cosy  = cos y
                                sinhx = sinh x
                                coshx = cosh x

        asin z@(x:+y)  =  y':+(-x')
                          where  (x':+y') = log (((-y):+x) + sqrt (1 - z*z))
        acos z         =  y'':+(-x'')
                          where (x'':+y'') = log (z + ((-y'):+x'))
                                (x':+y')   = sqrt (1 - z*z)
        atan z@(x:+y)  =  y':+(-x')
                          where (x':+y') = log (((1-y):+x) / sqrt (1+z*z))

        asinh z        =  log (z + sqrt (1+z*z))
        acosh z        =  log (z + (z+1) * sqrt ((z-1)/(z+1)))
        atanh z        =  0.5 * log ((1.0+z) / (1.0-z))

        log1p x@(a :+ b)
          | abs a < 0.5 && abs b < 0.5
          , u <- 2*a + a*a + b*b = log1p (u/(1 + sqrt(u+1))) :+ atan2 (1 + a) b
          | otherwise = log (1 + x)
        {-# INLINE log1p #-}

        expm1 x@(a :+ b)
          | a*a + b*b < 1
          , u <- expm1 a
          , v <- sin (b/2)
          , w <- -2*v*v = (u*w + u + w) :+ (u+1)*sin b
          | otherwise = exp x - 1
        {-# INLINE expm1 #-}

    instance Storable a => Storable (Complex a) where
        sizeOf a       = 2 * sizeOf (realPart a)
        alignment a    = alignment (realPart a)
        peek p           = do
                            q <- return $ castPtr p
                            r <- peek q
                            i <- peekElemOff q 1
                            return (r :+ i)
        poke p (r :+ i)  = do
                            q <-return $  (castPtr p)
                            poke q r
                            pokeElemOff q 1 i

    instance Applicative Complex where
      pure a = a :+ a
      f :+ g <*> a :+ b = f a :+ g b

    instance Monad Complex where
      a :+ b >>= f = realPart (f a) :+ imagPart (f b)