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MathGroup Archive 2005

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Re: Re: Nested iterators in Compile

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55058] Re: [mg55053] Re: [mg55010] Nested iterators in Compile
  • From: DrBob <drbob at bigfoot.com>
  • Date: Fri, 11 Mar 2005 04:20:33 -0500 (EST)
  • References: <200503101025.FAA19427@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

Hartmut,

Here's your own solution with a different result (due to 5.1.1, perhaps?):

f2=Compile[{{n,_Integer}},
       Module[{s=0},Do[Do[s+=j,{j,i}],{i,n}];s]];
f2[[-2]]

Function[{n},Module[{s=0},Do[Do[s+=j,{j,i}],{i,n}];s]]

FreeQ[f2[[-2]],Function]

False

If only I had some more of that "purposive pragmatism".

Bobby

On Thu, 10 Mar 2005 05:25:20 -0500 (EST), Wolf, Hartmut <Hartmut.Wolf at t-systems.com> wrote:

>
>> -----Original Message-----
>> From: Maxim [mailto:ab_def at prontomail.com]
To: mathgroup at smc.vnet.net
>> Sent: Wednesday, March 09, 2005 12:35 PM
>> Subject: [mg55058] [mg55053] [mg55010] Nested iterators in Compile
>>
>> The fact that iterators work differently when used in Compile
>> seems to
>> lead to a serious limitation:
>>
>> In[1]:=
>> Compile[{n},
>>   Module[{s = 0},
>>     Do[s += j, {i, n}, {j, i}];
>>     s
>> ]][10]
>>
>> CompiledFunction::cfse: Compiled expression i should be a
>> machine-size
>> real number.
>>
>> CompiledFunction::cfex: External evaluation error at instruction 4;
>> proceeding with uncompiled evaluation.
>>
>> Out[1]=
>> 220
>>
>> The iterator {j, i} is evaluated before any value is assigned
>> to i, and
>> the evaluation of the compiled code fails (and if we add the
>> initialization i=0 before Do, we'll only get an empty loop as
>> the result,
>> unlike the uncompiled version). So we have to resort to some
>> workarounds
>> such as changing the inner iterator to {j, n} and adding If[j>i,
>> Continue[]] to the loop body, which of course decreases the
>> performance.
>>
>> Maxim Rytin
>> m.r at inbox.ru
>>
>>
>
>
> Maxim,
>
> I had told you this before:
>
> using compiled functions needs some sort of purposive pragmatism.
> Also mistrust any compiled function f with
>
> In[3]:= FreeQ[f[[-2]], Function]
> Out[3]= False
>
>
> This case can be solved easily:
>In[4]:= f2 = Compile[{{n, _Integer}},
>            Module[{s = 0}, Do[Do[s += j, {j, i}], {i, n}];
>             s]];
>
> In[5]:= f2[10]
> Out[5]= 220
>
> In[6]:= FreeQ[f2[[-2]], Function]
> Out[6]= True
>
>
>
> --
> Hartmut Wolf
>
>
>
>



-- 
DrBob at bigfoot.com


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