Hi,
I have been doing probability theory tests. One of them involved the so
called "secretary problem". Here is my code:
>>>
module Main where
import Random
import List
import IO
type Process = [Integer] -> Bool
simulate :: Int -> Integer -> Process -> IO Double
simulate n m proc =
do tries <- accumulate [ map proc (randomIO (1,m)) | _ <- [1..n] ]
return (length (filter id tries) // n)
where
n // m = fromInt n / fromInt m
sim :: Int -> IO Double
sim k = simulate 1000 100 proc
where
proc rs = [best] == take 1 afterk
where
xs = take 100 (nub rs)
best = 100
bestk = maximum (take k xs)
afterk = dropWhile (< bestk) (drop k xs)
main :: IO ()
main =
do ps <- accumulate [ sim k | k <- [35..39] ]
print ps
<<<
When I run this module with ghc-4.01, I get _wrong_ results, and a bus
error:
>>>
[koen] -: ghc-4.01 -O secretary.hs -o secretary
ghc-4.01: module version changed to 2; reason: usages changed
[koen] -: secretary
[3.3e-2,0.0,0.0,0.354,0.174]
Bus error
<<<
The right behavior should be like:
>>>
[koen] -: hbc secretary.hs -o secretary
[koen] -: secretary
[0.398, 0.386, 0.376, 0.353, 0.363]
<<<
Or even:
>>>
Hugs> main
[0.366, 0.369, 0.383, 0.383, 0.379]
<<<
I am trying to find out if it is because of the random numbers, or because
of the use of -O. But these programs take ages to run...
Regards,
Koen.
--
Koen Claessen,
[EMAIL PROTECTED],
http://www.cs.chalmers.se/~koen,
Chalmers University of Technology.
