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-- Caused a crash in GHC 6.4 when optimising, due to inlining of runST too early.
-- Spectral Norm benchmark
import Data.Array
import System.Environment (getArgs)
main = do
--[arg] <- getArgs
--let n = (read arg) - 1
let n = 80
let init = listArray (0,n) (repeat 1.0)
let (v:u:rest) = drop 19 $ iterate (eval_AtA_times_u n) init
let vBv = sum [(u!i)*(v!i) |i<-[0..n]]
let vv = sum [(v!i)*(v!i) |i<-[0..n]]
print $ sqrt (vBv/vv)
eval_AtA_times_u n u = eval_At_times_u n v
where v = eval_A_times_u n u
eval_A x y = 1.0/((i+j)*(i+j+1)/2+i+1)
where i = fromIntegral x
j = fromIntegral y
eval_A_times_u n u = accumArray (+) 0 (0,n)
[(i,(eval_A i j) * u!j)|i<-[0..n], j<-[0..n]]
eval_At_times_u n u = accumArray (+) 0 (0,n)
[(i,(eval_A j i) * u!j)|i<-[0..n], j<-[0..n]]
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