[Haskell-cafe] Re: hmatrix's fitModel function crashes ghc(i)
aruiz at um.es
Sat Nov 6 16:12:25 EDT 2010
Roel van Dijk wrote:
> I would like to use hmatrix to do some function fitting with the
> Levenberg Marquardt algorithm. As an example I would like to fit the
> very simple function "f x = a*x + b" on some data points. The problem
> is that executing the 'fitModel' function crashes GHC(i) with a
> segmentation fault.
Can you reproduce it on a 32 bit machine?
There is a known problem with some hmatrix GSL wrappers on 64 bit in
interpreted mode. This is mentioned at the end of the install page:
In this case the segmentation fault happens inside a foreign GSL
function, only in interpreted code, and only in 64 bit. It does not
happen in compiled code. (Although I have a report of a similar
segmentation fault with compiled code if the output is redirected). I
don't really know how to debug this kind of problem. As a first step I
will try to obtain a minimal test case without any package dependencies.
This makes debugging difficult. Can anyone spot
> what I am doing wrong?
Your are doing nothing wrong. I will create a new, more visible page for
the known problems.
Given all the lists of Double's it seems very
> easy to make an error regarding the number of arguments with the model
> function or the derivative.
Static argument checking would be ideal, but at least they are normal
runtime errors and should never crash the program.
> Try to evaluate the 'test' function in the small program listed below.
> I would expect an output of [1, 0] (y = 1*x + 0) instead of a
> segmentation fault.
It works for me in 32 bit:
$ ghci Test.hs
GHCi, version 6.12.3: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
[1 of 1] Compiling Test ( Test.hs, interpreted )
Ok, modules loaded: Test.
Loading package filepath-18.104.22.168 ... linking ... done.
Loading package old-locale-22.214.171.124 ... linking ... done.
Loading package old-time-126.96.36.199 ... linking ... done.
Loading package unix-188.8.131.52 ... linking ... done.
Loading package directory-184.108.40.206 ... linking ... done.
Loading package process-220.127.116.11 ... linking ... done.
Loading package array-0.3.0.1 ... linking ... done.
Loading package storable-complex-0.2.1 ... linking ... done.
Loading package hmatrix-0.10.0.1 ... linking ... done.
[ 1.0, 0.0, 1.0, 0.0 ])
> Relevant versions:
> - hmatrix-0.10.0.0
> - gsl-1.14
> - ghc-6.12.3 (64 bit)
> Small program:
> module Test where
> -- from base:
> import Control.Arrow ( second )
> import Control.Applicative ( pure )
> -- from hmatrix:
> import Data.Packed.Matrix ( Matrix )
> import Numeric.GSL.Fitting ( FittingMethod(LevenbergMarquardt), fitModel )
> -- input list of (x, y) pairs, output coefficients of "f x = a x * b"
> fitLinear :: [(Double, Double)] -> ([Double], Matrix Double)
> fitLinear samples = fitModel 1
> (linearModel, linearDer)
> (map (second pure) samples)
> [0, 0]
> linearModel :: [Double] -> Double -> [Double]
> linearModel [a, b] x = [a*x + b, 0]
> linearModel _ x = error "wrong arguments"
> linearDer :: [Double] -> Double -> [[Double]]
> linearDer [_, _] x = [[x, 0]]
> linearDer _ _ = error "wrong arguments"
> test = fitLinear [(0,0), (1,1), (2,2)]
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