Re: Compile function and AppendTo for lists (vrs.

• To: mathgroup at smc.vnet.net
• Subject: [mg124704] Re: Compile function and AppendTo for lists (vrs.
• From: Fred Simons <f.h.simons at tue.nl>
• Date: Wed, 1 Feb 2012 03:50:50 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <201201311039.FAA01093@smc.vnet.net>

Hi Patrick,

Op 31-1-2012 11:39, Patrick Scheibe schreef:
> Hi Fred,
>
> some short notes:
>
>
>> appendBag2a = Compile[{{k, _Integer, 0}}, Module[{p = Bag[Most[{0}]]},
>>       Do[StuffBag[p, Bag[{1, i}]], {i, 1, k}];
>>       Table[BagPart[BagPart[p, i], All], {i, 1, k}]]];
>>
>> That works fine and fast,
> But look that your type p is clearly wrong. p is a bag of bags of
> Integer and has to be initialized with
>
> Internal`Bag[Most[{Internal`Bag[{1}]}]]
>
> We can only guess about the reasons why it works anyway. If it is
> implemented with pointers, than it seems the integers of your p-Bag are
> used to store the pointers.
Clearly wrong is not quite clearly wrong. Indeed, with

p = Bag[Most[{0}]]}

we define p to be a bag with argument a list of integers. The fact that the implementation works suggests that in such a situation not only integers but also bags with integers are allowed as elements of the list.

>
>> The problem seems to be the initialization of the
>> locale variable p. I tried compilation with the definitions p=Bag[],
>> p=Bag[{}], p=Bag[Rest[{0}]], p=Bag[Rest[{{0,0}}]], or e.g.
> Now you know how.
No, not really.  Inspired by your remarks, I did some further tests with
compiling functions containing a Bag, and it seems to be that that the
compiled function runs smoothly only when the argument of Bag is a list
of reals or a list of integers (maybe containing bags of reals or bags
of integers). So when it is a list of a list of integers, as in the
function I was trying to compile, the compiled function will always
proceed with the uncompiled version.

In your function appendBag2 you use a Bag with Bag's inside the argument
list. That is a very interesting idea. However, there is a big
disadvantage: at the and the resulting expression will contain many
Bag's. Since each Bag points to a raw expression stored somewhere, the
amount of memory that is needed can be tremendous. In some of my tests
indeed the kernel closed because of lack of memory.  So my feeling is
that it is better not to use this technique and instead to flatten the
tensor to a list, and at the end use the function Partition fo find the
tensor you are looking for. In this way, only one Bag is needed, thus
not requiring an excessive amount of memory, and the compiled function
will run smoothly.
>
> Cheers
> Patrick
>
>
Once again many thanks and best wishes,

Fred

• Prev by Date: Re: large lists with variable and if condition (vrs. 8.0.4)
• Next by Date: Re: large lists with variable and if condition (vrs. 8.0.4)
• Previous by thread: Re: large lists with variable and if condition (vrs. 8.0.4)
• Next by thread: Re: Compile function and AppendTo for lists (vrs. 8.0.4)