[Cs254f11] length of individual thoughts...
Lee Spector
lspector at hampshire.edu
Fri Dec 2 14:46:54 EST 2011
Ah, you have come to a pretty deep vein of genetic programming research, on bloat control methods (of which this is one, for which you could use a fancy name like "lexicographic parsimony pressure").
Short answer: Maybe! Depends! On what? Not sure! It'll usually make things smaller but at what cost in terms of problem solving?
Somewhat longer: Certainly a good idea to try sometimes. Or if you're mainly interested in readability then you might do it only late in a run (on which there's some literature).
The tip of the iceberg: In my journal we've just published a new and I think very good contribution to the bloat literature, which includes a good overview of related work. I've put a link to it on the class moodle page, with the name "Silva et al. GPEM article on bloat" (it's with the other links under the syllabus info, above the calendar).
-Lee
On Dec 2, 2011, at 2:33 PM, Wm. Josiah Erikson wrote:
> Hehe. Yes. Now I pose an interesting question (well, at least *I* think it's interesting):
>
> Does doing this in one's tournament selection (preferring smaller individuals with the same error) prevent program bloat? (Yes, I think, from preliminary experiments) And does it inhibit evoluation?
>
> I'm not sure yet on the second question, but I think the answer is probably yes as well. It certainly does with small population sizes, like 100 - you just hit a local minimum and sit there almost immediately. With a population size of 1000, given what I'm doing, it seems less clear that this is occurring, and the things I'm getting are certainly a lot shorter and more readable! This doesn't necessarily mean they are better, but perhaps it's easier to discern what they are actually doing and if it's at all interesting (probably not).
>
> -Josiah
>
>
>
> On 12/2/11 2:16 PM, Lee Spector wrote:
>> On Dec 2, 2011, at 2:02 PM, Wm. Josiah Erikson wrote:
>>
>>> You interpreted what I was doing correctly, and actually that "mistake" you pointed out was intentional, because to do it "right", the line gets even more insane:
>>>
>>> (first (first (sort #(< (codesize (first %1)) (codesize (first %2))) (filter #(= (second %) (second (first sorted))) sorted))))
>>>
>>> And it doesn't gain you anything.
>>>
>> Yeah, well...... in a sense, but in another it gains you clarity of purpose when you try to read/change your code, which is actually pretty valuable.
>>
>>
>>> But I don't quite know how to write the second thing you suggest. Let's take a stab:
>>>
>>> (let
>>> [sorted (sort (fn [[prog1 err1] [prog2 err2]] (or (< err1 err2)(< (codesize prog1) (codesize prog2)))) population)]
>> Close, but not quite.
>>
>> First, let's reformat this -- I can't stress enough how much this can help, at least for me, and I suspect for everyone:
>>
>> (let [sorted (sort (fn [[prog1 err1] [prog2 err2]]
>> (or (< err1 err2)
>> (< (codesize prog1)
>> (codesize prog2))))
>> population)]
>>
>> We're sorting population by a function of two arguments that are destructured into program/error pairs, and the guts of the thing is:
>>
>> (or (< err1 err2)
>> (< (codesize prog1)
>> (codesize prog2)))
>>
>> So you're telling sort that pair number 1 comes before pair number 2 if its error is lower OR its size is smaller. Which means it'll make it come first if it's smaller, even if it's ... AHA -- you discovered this and emailed me mid sentence!
>>
>> Now you propose (reformatted!):
>>
>> (let
>> [sorted (sort (fn [[prog1 err1] [prog2 err2]]
>> (or (< err1 err2)
>> (and (< (codesize prog1) (codesize prog2))
>> (= err1 err2))))
>> population)]
>>
>> And that looks right to me!
>>
>> -Lee
>>
>>
>>
>>
>>
>>> ...
>>>
>>> I think that's what you meant, and is, indeed, a better idea. Thanks :)
>>>
>>> -Josiah
>>>
>>>
>>>
>>> On 12/2/11 12:20 PM, Lee Spector wrote:
>>>> Close.... or rather, I think it will work but slightly by accident.
>>>>
>>>> I'm assuming that "sorted" here contains a sequence of [program error] pairs -- note that in some of my example code I had those pairs the other way around, so make sure you're treating them consistently!
>>>>
>>>> In any event, with that assumption (which is the only thing that makes sense given the rest of your code) your call to filter is producing a sequence of only those that have the same error as the first one (which will be the best). Then you're sorting those on the basis of which has the lowest codesize, but you're calling codesize on the whole pairs rather than on just the programs. Which I guess always comes to the same thing, since the error will just add 1 to everything uniformly. So it'll do the right thing but not quite in the right way (which you could do by calling codesize on just the programs).
>>>>
>>>> Alternatively, and this is probably what I'd do, you could change the predicate used in the call to sort that gives a value to "sorted" it say that %1 should come before %2 if either %1 has a lower error OR if they have the same error by the program in %1 has a lower codesize.
>>>>
>>>> -Lee
>>>>
>>>>
>>>> On Dec 2, 2011, at 11:24 AM, Wm. Josiah Erikson wrote:
>>>>
>>>>> So in the way I'm evolving things, I've often got a population full of individuals with similar error. Given Lee's
>>>>>
>>>>> (let [sorted (sort #(< (second %1) (second %2)) population)]
>>>>>
>>>>> would this function get the smallest individual that had the best error? :
>>>>>
>>>>> (first (first (sort #(< (codesize %1) (codesize %2)) (filter #(= (second %) (second (first sorted))) sorted))))
>>>>>
>>>>> (It seems to work)
>>>>>
>>>>> Is there an easier way to do that? Is this even a good idea? I'm currently just using it as the final return value so that my final result is as easy to read as possible :)
>>>>> _______________________________________________
>>>>> Cs254f11 mailing list
>>>>> Cs254f11 at lists.hampshire.edu
>>>>> https://lists.hampshire.edu/mailman/listinfo/cs254f11
>>>> --
>>>> Lee Spector, Professor of Computer Science
>>>> Cognitive Science, Hampshire College
>>>> 893 West Street, Amherst, MA 01002-3359
>>>> lspector at hampshire.edu, http://hampshire.edu/lspector/
>>>> Phone: 413-559-5352, Fax: 413-559-5438
>>>>
>>>> _______________________________________________
>>>> Cs254f11 mailing list
>>>> Cs254f11 at lists.hampshire.edu
>>>> https://lists.hampshire.edu/mailman/listinfo/cs254f11
>>> --
>>> Wm. Josiah Erikson
>>> Network Engineer
>>> Hampshire College
>>> Amherst, MA 01002
>>> (413) 559-6091
>>>
>>> _______________________________________________
>>> Cs254f11 mailing list
>>> Cs254f11 at lists.hampshire.edu
>>> https://lists.hampshire.edu/mailman/listinfo/cs254f11
>> --
>> Lee Spector, Professor of Computer Science
>> Cognitive Science, Hampshire College
>> 893 West Street, Amherst, MA 01002-3359
>> lspector at hampshire.edu, http://hampshire.edu/lspector/
>> Phone: 413-559-5352, Fax: 413-559-5438
>>
>
> --
> Wm. Josiah Erikson
> Network Engineer
> Hampshire College
> Amherst, MA 01002
> (413) 559-6091
>
--
Lee Spector, Professor of Computer Science
Cognitive Science, Hampshire College
893 West Street, Amherst, MA 01002-3359
lspector at hampshire.edu, http://hampshire.edu/lspector/
Phone: 413-559-5352, Fax: 413-559-5438
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