Activation.hs

-- |
-- Module:     AI.Instinct.Activation
-- Copyright:  (c) 2011 Ertugrul Soeylemez
-- License:    BSD3
-- Maintainer: Ertugrul Soeylemez <es@ertes.de>
--
-- Activation functions.

module AI.Instinct.Activation
    ( -- * Type
      Activation(..),
      actFunc,
      actDeriv
    )
    where


-- | Activation functions.

data Activation
    = LogisticAct    -- ^ Logistic activation.
    deriving (Read, Show)


-- | Apply an activation function.

actFunc :: Activation -> Double -> Double
actFunc LogisticAct = logistic


-- | Apply the derivative of an activation function.

actDeriv :: Activation -> Double -> Double
actDeriv LogisticAct x = let lx = logistic x in lx * (1 - lx)


-- | This is the logistic activation function.

logistic :: Double -> Double
logistic x = 1 / (1 + exp (-x))