Re: [Haskell-cafe] Sorting efficiency
Hi David, can this help you? http://www.scribd.com/doc/81029312/5/Sorting-pairwise-sums Heinrich Am 04.08.2012 20:47, schrieb David Feuer: I realized my algorithm is insane. The correct way to sort [a*b|a-A, b-B] is clearly to sort A and B, then for each a in A construct either map (a*) B or map (a*) (reverse B), depending on the sign of a, then merge all these results together with a merge that collapses duplicates. I was multiplying and then sorting, which is way worse. The same (modulo sign) goes for adding lists. On Aug 4, 2012 1:55 PM, Clark Gaebel cgae...@uwaterloo.ca [6] wrote: Its generally not advisable to use Data.List for performance-sensitive parts of an application. Try using Data.Vector instead: http://hackage.haskell.org/package/vector [4] On Sat, Aug 4, 2012 at 11:23 AM, David Feuer david.fe...@gmail.com [5] wrote: Im writing a toy program (for a SPOJ problem--see https://www.spoj.pl/problems/ABCDEF/ [1] ) and the profiler says my performance problem is that Im spending too much time sorting. Im using Data.List.sort on [Int32] (its a 32-bit architecture). Others, using other languages, have managed to solve the problem within the time limit using the same approach Ive taken (I believe), but mine is taking too long. Any suggestions? Do I need to do something insane like sorting in an STUArray? David Feuer ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org [2] http://www.haskell.org/mailman/listinfo/haskell-cafe [3] Links: -- [1] https://www.spoj.pl/problems/ABCDEF/ [2] mailto:Haskell-Cafe@haskell.org [3] http://www.haskell.org/mailman/listinfo/haskell-cafe [4] http://hackage.haskell.org/package/vector [5] mailto:david.fe...@gmail.com [6] mailto:cgae...@uwaterloo.ca ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sorting efficiency
Unfortunately, I doubt it can. That algorithm reduces the number of
comparisons a good bit, but the asymptotic complexity of its other
operations remains the same, with apparently bad constant factors
(according to the article). Also, that article describes the algorithm
in terms of sorting [a+b| a-A, b-A], whereas I'm actually dealing
(in the more substantial phase) with [a+b | a-A, b-B], where B is
much larger than A. Using the merging approach I described in my last
email, I can reduce the complexity from mn log(mn) in the naive
algorithm to mn log (min {m,n}). Since m=100 and n~=10,000, I should
be able to get nearly double the speed of the naive approach, as long
as my multi-merge is fast enough.
On Sun, Aug 5, 2012 at 3:59 AM, Heinrich Hördegen
hoerde...@funktional.info wrote:
Hi David,
can this help you?
http://www.scribd.com/doc/81029312/5/Sorting-pairwise-sums
Heinrich
Am 04.08.2012 20:47, schrieb David Feuer:
I realized my algorithm is insane. The correct way to sort [a*b|a-A,
b-B] is clearly to sort A and B, then for each a in A construct
either map (a*) B or map (a*) (reverse B), depending on the sign of a,
then merge all these results together with a merge that collapses
duplicates. I was multiplying and then sorting, which is way worse.
The same (modulo sign) goes for adding lists.
On Aug 4, 2012 1:55 PM, Clark Gaebel cgae...@uwaterloo.ca [6]
wrote:
Its generally not advisable to use Data.List for
performance-sensitive parts of an application.
Try using Data.Vector instead:
http://hackage.haskell.org/package/vector [4]
On Sat, Aug 4, 2012 at 11:23 AM, David Feuer david.fe...@gmail.com
[5] wrote:
Im writing a toy program (for a SPOJ problem--see
https://www.spoj.pl/problems/ABCDEF/ [1] ) and the profiler says
my
performance problem is that Im spending too much time sorting. Im
using Data.List.sort on [Int32] (its a 32-bit architecture).
Others,
using other languages, have managed to solve the problem within
the
time limit using the same approach Ive taken (I believe), but
mine is
taking too long. Any suggestions? Do I need to do something
insane
like sorting in an STUArray?
David Feuer
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Links:
--
[1] https://www.spoj.pl/problems/ABCDEF/
[2] mailto:Haskell-Cafe@haskell.org
[3] http://www.haskell.org/mailman/listinfo/haskell-cafe
[4] http://hackage.haskell.org/package/vector
[5] mailto:david.fe...@gmail.com
[6] mailto:cgae...@uwaterloo.ca
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Re: [Haskell-cafe] Sorting efficiency
Where by nearly double, of course, I really mean nearly triple.
I'm a little tired.
David
On Sun, Aug 5, 2012 at 5:37 AM, David Feuer david.fe...@gmail.com wrote:
Unfortunately, I doubt it can. That algorithm reduces the number of
comparisons a good bit, but the asymptotic complexity of its other
operations remains the same, with apparently bad constant factors
(according to the article). Also, that article describes the algorithm
in terms of sorting [a+b| a-A, b-A], whereas I'm actually dealing
(in the more substantial phase) with [a+b | a-A, b-B], where B is
much larger than A. Using the merging approach I described in my last
email, I can reduce the complexity from mn log(mn) in the naive
algorithm to mn log (min {m,n}). Since m=100 and n~=10,000, I should
be able to get nearly double the speed of the naive approach, as long
as my multi-merge is fast enough.
On Sun, Aug 5, 2012 at 3:59 AM, Heinrich Hördegen
hoerde...@funktional.info wrote:
Hi David,
can this help you?
http://www.scribd.com/doc/81029312/5/Sorting-pairwise-sums
Heinrich
Am 04.08.2012 20:47, schrieb David Feuer:
I realized my algorithm is insane. The correct way to sort [a*b|a-A,
b-B] is clearly to sort A and B, then for each a in A construct
either map (a*) B or map (a*) (reverse B), depending on the sign of a,
then merge all these results together with a merge that collapses
duplicates. I was multiplying and then sorting, which is way worse.
The same (modulo sign) goes for adding lists.
On Aug 4, 2012 1:55 PM, Clark Gaebel cgae...@uwaterloo.ca [6]
wrote:
Its generally not advisable to use Data.List for
performance-sensitive parts of an application.
Try using Data.Vector instead:
http://hackage.haskell.org/package/vector [4]
On Sat, Aug 4, 2012 at 11:23 AM, David Feuer david.fe...@gmail.com
[5] wrote:
Im writing a toy program (for a SPOJ problem--see
https://www.spoj.pl/problems/ABCDEF/ [1] ) and the profiler says
my
performance problem is that Im spending too much time sorting. Im
using Data.List.sort on [Int32] (its a 32-bit architecture).
Others,
using other languages, have managed to solve the problem within
the
time limit using the same approach Ive taken (I believe), but
mine is
taking too long. Any suggestions? Do I need to do something
insane
like sorting in an STUArray?
David Feuer
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org [2]
http://www.haskell.org/mailman/listinfo/haskell-cafe [3]
Links:
--
[1] https://www.spoj.pl/problems/ABCDEF/
[2] mailto:Haskell-Cafe@haskell.org
[3] http://www.haskell.org/mailman/listinfo/haskell-cafe
[4] http://hackage.haskell.org/package/vector
[5] mailto:david.fe...@gmail.com
[6] mailto:cgae...@uwaterloo.ca
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[Haskell-cafe] Sorting efficiency
I'm writing a toy program (for a SPOJ problem--see https://www.spoj.pl/problems/ABCDEF/ ) and the profiler says my performance problem is that I'm spending too much time sorting. I'm using Data.List.sort on [Int32] (it's a 32-bit architecture). Others, using other languages, have managed to solve the problem within the time limit using the same approach I've taken (I believe), but mine is taking too long. Any suggestions? Do I need to do something insane like sorting in an STUArray? David Feuer ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sorting efficiency
It's generally not advisable to use Data.List for performance-sensitive parts of an application. Try using Data.Vector instead: http://hackage.haskell.org/package/vector On Sat, Aug 4, 2012 at 11:23 AM, David Feuer david.fe...@gmail.com wrote: I'm writing a toy program (for a SPOJ problem--see https://www.spoj.pl/problems/ABCDEF/ ) and the profiler says my performance problem is that I'm spending too much time sorting. I'm using Data.List.sort on [Int32] (it's a 32-bit architecture). Others, using other languages, have managed to solve the problem within the time limit using the same approach I've taken (I believe), but mine is taking too long. Any suggestions? Do I need to do something insane like sorting in an STUArray? David Feuer ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sorting efficiency
I realized my algorithm is insane. The correct way to sort [a*b|a-A, b-B] is clearly to sort A and B, then for each a in A construct either map (a*) B or map (a*) (reverse B), depending on the sign of a, then merge all these results together with a merge that collapses duplicates. I was multiplying and then sorting, which is way worse. The same (modulo sign) goes for adding lists. On Aug 4, 2012 1:55 PM, Clark Gaebel cgae...@uwaterloo.ca wrote: It's generally not advisable to use Data.List for performance-sensitive parts of an application. Try using Data.Vector instead: http://hackage.haskell.org/package/vector On Sat, Aug 4, 2012 at 11:23 AM, David Feuer david.fe...@gmail.comwrote: I'm writing a toy program (for a SPOJ problem--see https://www.spoj.pl/problems/ABCDEF/ ) and the profiler says my performance problem is that I'm spending too much time sorting. I'm using Data.List.sort on [Int32] (it's a 32-bit architecture). Others, using other languages, have managed to solve the problem within the time limit using the same approach I've taken (I believe), but mine is taking too long. Any suggestions? Do I need to do something insane like sorting in an STUArray? David Feuer ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
