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MathGroup Archive 2005

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Re: Re: letrec/named let

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56863] Re: [mg56848] Re: letrec/named let
  • From: DrBob <drbob at bigfoot.com>
  • Date: Sun, 8 May 2005 02:10:14 -0400 (EDT)
  • References: <200505071935.PAA26955@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

So the latest version of Ordering has a large performance bug on Windows,
but not Mac.

Could someone test it with Linux?

Bobby

On Sat, 7 May 2005 15:35:09 -0400 (EDT), Bill Rowe <readnewsciv at earthlink.net> wrote:

> On 5/7/05 at 4:17 AM, drbob at bigfoot.com (DrBob) wrote:
>
>> Indeed, for real data, your substitute for ordering is much faster
>> (in 5.1.1) than the built-in. If it's 2.5 times SLOWER on your
>> machine, that does seem to imply WRI has radically DECREASED
>> Ordering's performance from 4.1 to 5.1.1.
>>
>> It's hard to believe they'd do that, but apparently they have.
>>
>>> The only possibility I can think of is that ord=Ordering[data]
>>> returns a packed array of integers when data is integer, while
>>> ord=Ordering[data] returns an unpacked array of integers when data
>>> is real.
>>
>> Exactly right. See below. Maybe this explains the performance issue
>> for Ordering itself, too.
>>
>> (Note: 'data' is packed in both tests.)
>>
>> pq = Developer`PackedArrayQ; carlTimed[s_] := Module[{ord, t, o,
>> ans},
>> Print@Timing[ord = Ordering@s; Ordering]; Print@Timing[t =
>> FoldList[ Plus, 1, Sign[Abs[ListCorrelate[{1, -1}, s[[ord]]]]]];
>> FoldList]; Print@Timing[o = Ordering@ord; Ordering];
>> Print@Timing[ans = t[[o]]; Part]; Print[pq /@ {ord, t, o, ans}];
>> ans]
>> ordering[x_List] := Round@Sort[Transpose[{x,
>> N@Range@Length@x}]][[All, 2]] carlNewOrder[s_] := Module[{ord, t,
>> o, ans},
>> Print@Timing[ord = ordering@s; ordering]; Print@Timing[ t =
>> FoldList[Plus, 1, Sign[Abs[ListCorrelate[{1, -1}, s[[ord]]]]]];
>> FoldList]; Print@Timing[o = ordering@ord; ordering];
>> Print@Timing[ans = t[[o]]; Part]; Print[pq /@ {ord, t, o, ans}];
>> ans]
>>
>> data = Table[Random[], {10^6}]; Timing[carlTimed@data; Total]
>> Timing[carlNewOrder@data; Total]
>>
>> {8. Second,Ordering} {0.391 Second,FoldList} {7.25 Second,Ordering}
>> {0.063 Second,Part} {False,True,True,True} {15.891 Second,Total}
>>
>> {1.063 Second,ordering} {0.343 Second,FoldList} {7.36
>> Second,ordering} {0.062 Second,Part} {True,True,True,True} {8.828
>> Second,Total}
>>
>> Notice ordering returned a packed array (ord) for real data, but
>> Ordering didn't. Also notice the second use (with Integer data) has
>> Ordering and ordering equally fast, but that's despite ordering
>> being applied to a packed integer array, but Ordering applied to an
>> unpacked array.
>
> Interesting. These results seem very dependent on platform. Specifically, when I run the code above I get.
>
> In[5]:=
> data = Table[Random[], {10^6}];
> Timing[carlTimed[data]; Total]
> Timing[carlNewOrder[data]; Total]
>
> {1.478287*Second, Ordering}
> {1.596432*Second, FoldList}
> {1.215809*Second, Ordering}
> {0.262963*Second, Part}
> {True, True, True, True}
> {4.568661*Second, Total}
>
> {3.336485*Second, ordering}
> {1.603586*Second, FoldList}
> {18.20541*Second, ordering}
> {0.266754*Second, Part}
> {True, True, True, True}
> {23.426852*Second, Total}
>
> In[8]:=
> $Version
> Out[8]=
> "5.1 for Mac OS X (January 27, 2005)"
>
> As you can see on my machine, both Ordering and ordering return packed arrays. And when I compare timings of Carl's solution to yours I get results consistent with what Carl reported, i.e., his solution runs about 5 times faster.
> --
> To reply via email subtract one hundred and four
>
>
>
>



-- 
DrBob at bigfoot.com


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