[Haskell-cafe] Inductive graphs memory usage

[Andre Nathan]

Hello

I'm trying to create a directed graph using the Data.Graph.Inductive.
The graph is a random graph using the G(n, p) model, that is, each of
the n nodes is linked to every other node with probability p.

I'm seeing a large increase of memory usage when n grows (this is using
p = 0.1):

n = 1000 ->  96MB
n = 2000 -> 283MB
n = 3000 -> 760MB

So, I'm probably doing something very stupid :) The code is below. Is
there anything I could do to optimize memory usage here?

  module Main where

  import Control.Monad
  import Data.Graph.Inductive
  import System.Random

  createEdges :: Int -> Double -> IO [LEdge Int]
  createEdges n prob = foldM create [] [1..n]
    where create es i = foldM (flip $ link i) es [i, i-1 .. 1]
          link i j es | i == j    = return es  -- no self-loops
                      | otherwise = do
                          es'  <- maybeCreateEdge i j prob es
                          es'' <- maybeCreateEdge j i prob es'
                          return es''

  maybeCreateEdge :: Node -> Node -> Double -> [LEdge Int]
                  -> IO [LEdge Int]
  maybeCreateEdge i j prob es = do
    r <- randomDouble
    return $ if r < prob then (i, j, 0):es else es

  randomDouble :: IO Double
  randomDouble = getStdRandom $ random

  main :: IO ()
  main = do
    let (n, p) = (3000, 0.1)
    es <- createEdges n p
    let g = mkGraph [(i, 0) | i <- [1..n]] es :: Gr Int Int
    return ()


Thanks,
Andre