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|
-----------------------------------------------------------------------------
-- |
-- Module : XMonadContrib.Anneal
-- Copyright : (c) David Roundy
-- License : BSD-style (see LICENSE)
--
-- Maintainer : David Roundy <droundy@darcs.org>
-- Stability : unstable
-- Portability : unportable
--
--
-----------------------------------------------------------------------------
module XMonadContrib.Anneal ( Rated(Rated), the_value, the_rating
, anneal, annealMax ) where
import System.Random ( StdGen, Random, mkStdGen, randomR )
import Control.Monad.State ( State, runState, put, get, gets, modify )
data Rated a b = Rated !a !b
deriving ( Show )
instance Functor (Rated a) where
f `fmap` (Rated v a) = Rated v (f a)
the_value :: Rated a b -> b
the_value (Rated _ b) = b
the_rating :: Rated a b -> a
the_rating (Rated a _) = a
instance Eq a => Eq (Rated a b) where
(Rated a _) == (Rated a' _) = a == a'
instance Ord a => Ord (Rated a b) where
compare (Rated a _) (Rated a' _) = compare a a'
anneal :: a -> (a -> Double) -> (a -> [a]) -> Rated Double a
anneal st r sel = runAnneal st r (do_anneal sel)
annealMax :: a -> (a -> Double) -> (a -> [a]) -> Rated Double a
annealMax st r sel = runAnneal st (negate . r) (do_anneal sel)
do_anneal :: (a -> [a]) -> State (Anneal a) (Rated Double a)
do_anneal sel = do sequence_ $ replicate 100 da
gets best
where da = do select_metropolis sel
modify $ \s -> s { temperature = temperature s *0.99 }
data Anneal a = A { g :: StdGen
, best :: Rated Double a
, current :: Rated Double a
, rate :: a -> Rated Double a
, temperature :: Double }
runAnneal :: a -> (a -> Double) -> State (Anneal a) b -> b
runAnneal start r x = fst $ runState x (A { g = mkStdGen 137
, best = Rated (r start) start
, current = Rated (r start) start
, rate = \xx -> Rated (r xx) xx
, temperature = 1.0 })
select_metropolis :: (a -> [a]) -> State (Anneal a) ()
select_metropolis x = do c <- gets current
a <- select $ x $ the_value c
metropolis a
metropolis :: a -> State (Anneal a) ()
metropolis x = do r <- gets rate
c <- gets current
t <- gets temperature
let rx = r x
boltz = exp $ (the_rating c - the_rating rx) / t
if rx < c then do modify $ \s -> s { current = rx, best = rx }
else do p <- getOne (0,1)
if p < boltz
then modify $ \s -> s { current = rx }
else return ()
select :: [a] -> State (Anneal a) a
select [] = the_value `fmap` gets best
select [x] = return x
select xs = do n <- getOne (0,length xs - 1)
return (xs !! n)
getOne :: (Random a) => (a,a) -> State (Anneal x) a
getOne bounds = do s <- get
(x,g') <- return $ randomR bounds (g s)
put $ s { g = g' }
return x
|
