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Re: Compile can't handle indexed variables inside loops

  • To: mathgroup at smc.vnet.net
  • Subject: [mg114313] Re: Compile can't handle indexed variables inside loops
  • From: Oliver Ruebenkoenig <ruebenko at wolfram.com>
  • Date: Tue, 30 Nov 2010 06:23:28 -0500 (EST)

On Tue, 30 Nov 2010, Leonid Shifrin wrote:

> Hi Frank,
>
> This looks like a bug. I tried For loop with the same effect. I am actually
> surprised that Compile at all allows indexed variables.
>
> Regards,
> Leonid

Frank,

Yes, perhaps Compile shoud give a message like so:

fc1 = Module[{x[1], x[2]}, x[1] + x[2]]

Oliver

>
>
> On Mon, Nov 29, 2010 at 2:08 PM, Frank K <fkampas at gmail.com> wrote:
>
>> Indexed variables are renamed.  This is ok if they aren't inside a
>> loop
>>
>> In[1]:= fc1 = Compile[{x[1],x[2]},x[1]+x[2]]
>>
>> Out[1]= CompiledFunction[{x$651,x$652},x$651+x$652,-CompiledCode-]
>>
>> In[2]:= fc1[1,2]
>>
>> Out[2]= 3.
>>
>> Indexed variables are not renamed inside a loop, so the function
>> fails.
>>
>> In[3]:= fc2 = Compile[{x[1],x[2]},Sum[x[i],{i,2}]]
>>
>> Out[3]= CompiledFunction[{x$655,x$656},\!\(
>> \*UnderoverscriptBox[\(\[Sum]\), \(i\), \(2\)]\(x[i]\)\),-
>> CompiledCode-]
>>
>> In[4]:= fc2[1,2]
>> During evaluation of In[4]:= CompiledFunction::cfex: Could not
>> complete external evaluation at instruction 5;
>> proceeding with uncompiled evaluation. >>
>>
>> Out[4]= x[1]+x[2]
>>
>>
>


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