On Tuesday 25 January 2011 22:05:34, gutti wrote:
Hi,
I created some code from scratch - probably "ugly" beginners style - so I'm keen to get tips how to make it more pretty and faster
Cheers Phil
import Data.List
-- Input Data xi :: [Double] xi = [0 .. 10] yi :: [Double] yi = [2, 3, 5, 6, 7, 8, 9, 10 , 9, 8, 7] x = 11 :: Double
-- Functions limIndex xi idx | idx < 0 = 0 | idx > (length xi)-2 = (length xi)-2 | otherwise = idx
limIndex xi idx = max 0 (min idx (length xi - 2)) not necessarily better, but different
getIndex xi x = limIndex xi (maybe (length xi) id (findIndex (>x) xi)-1)
maybe val id is the same as fromMaybe val
getPnts xi yi idx = [xi !! idx, xi !! (idx+1), yi !! idx, yi !! (idx+1)]
getPnts xi yi idx = case drop idx $ zip xi yi of ((x1,y1):(x2,y2):_) -> [x1,x2,y1,y2] _ -> error "Not enough points"
interp xi yi x = let pts = getPnts xi yi (getIndex xi x) in (pts!!3-pts!!2)/(pts!!1-pts!!0)*(x-pts!!0)+pts!!2
let (x1:x2:y1:y2:_) = getPnts xi yi (getIndex xi x) in (y2 - y1)/(x2 - x1)*(x-x1) + y1
-- Calc y = interp xi yi x
main = do -- Output Data print (y)