[Haskell-cafe] Memory Management and Lists

[Christopher Howard]

I guess I was hesitating on posting the entire program source code in an
cafe email. I suppose I could send you a tarball, if you really wanted it...

Matrix is from Data.Matrix
<http://hackage.haskell.org/package/matrix-0.3.5.0/docs/Data-Matrix.html>.

It is hard to understand how thunks alone would explain it... there
would be at most 2000 thunks, right? Unless... Could there be a thunk
for every single call to getElem? That would be a lot of thunks!

Somebody suggested adding some strictness here... could you elaborate on
that? I tried inserting seq, but I didn't really understand how I was
supposed to use it...

On 07/12/2016 10:40 AM, Tom Ellis wrote:
> I can't run this code because it's missing several things, including the
> definition of Matrix and walk, and imports.
> 
> Certainly you are building up a large chain of thunks repeatedly applying
> the calculation for nMatrix, but how to solve it I cannot say without more
> information.
> 
> On Mon, Jul 11, 2016 at 07:01:24AM -0800, Christopher Howard wrote:
>> -- I'm a bit embarrassed of this code because I haven't yet optimized
>> -- the 'stamp' algorithm for reduced number of matrix operations. But
>> -- even in this state I should think the memory requirements shouldn't
>> -- exceed 1MB while generating the nth Matrix, unless Matrix n-1, n-2,
>> -- etc. are being preserved in memory unnecessarily.
>>
>> -- Monad Stack
>>
>> type StateReader s c a = StateT s (Reader c) a
>>
>> evalStateReader m s c = (runReader (evalStateT m s)) c
>>
>> -- Helper function
>>
>> type Point = (Float, Float)
>> type Metric = Point -> Point -> Float
>>
>> euclidean :: Metric
>> euclidean (x1, y1) (x2, y2) = sqrt ((x2 - x1)**2 + (y2 - y1)**2)
>>
>> -- monadic function. haven't had chance yet to optimize algorithm to
>> -- reduce number of matrix operations
>>
>> stamp = do radius <- ask
>>            (oMatrix, walk) <- get
>>            (wX, wY) <- (return . head) walk
>>            let nMatrix = matrix (nrows oMatrix) (ncols oMatrix)
>>                  (\(x, y) -> let (x', y') = (fromIntegral x, fromIntegral y)
>>                              in if euclidean (x', y') (wX, wY) > radius
>>                                 then getElem x y oMatrix
>>                                 else getElem x y oMatrix + 1)
>>              in put (nMatrix, tail walk) >> get
>>
>>
>>
>> -- sequences and gathers results as list
>>
>> stampingStates initMx radius walk =
>>   map fst $ evalStateReader (sequence (repeat stamp)) (initMx, walk) radius
>>
>>
>> -- Some quick experimentation code. h is the list
>>
>> h = stampingStates initMx radius walk'
>>   where initMx = zero 250 250
>>         radius = 40
>>         walk' = walk 40 (125, 125) (mkStdGen 31415)
>>
>> -- get 2001st Matrix and convert to Gloss Picture, employing
>> -- some color interpretation code
>>
>> intensityG = let mx = head (drop 2000 h)
>>              in toImage mx (lightnessInt 272 (minMax mx))
>>
>>
>> On 07/10/2016 10:30 AM, Tom Ellis wrote:
>>> On Sun, Jul 10, 2016 at 07:41:31AM -0800, Christopher Howard wrote:
>>>> issue: a Matrix itself should only be, I'm guessing, somewhere around
>>>> 100KB. But instead I'm maxing out the 3GB of RAM on my old T60 laptop.
>>>> Maybe I'm generating list elements (Matrices) a lot faster than memory
>>>> management is releasing them...?
>>>
>>> You have almost certainly got a space leak.  Can you post your code?
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