forgotten '^' of course

SequenceableCollection>>polynomialEval: thisX
  ^ self reverse inject: 0 into: [:sum :each | thisX * sum + each]


On Thu, Aug 4, 2011 at 01:38, Enrico Spinielli
<enrico.spinielli at googlemail.com> wrote:
> Levente (and all),
> what do you think about implementing SequenceableCollection>>polynomialEval:
> as follows:
>
> SequenceableCollection>>polynomialEval: thisX
>   self reverse inject: 0 into: [:sum :each | thisX * sum + each]
>
>
> The above version uses Horner's rule [1] and reads simpler IMHO.
> Of course reverse is needed only because the convention is to have
> the constant term as first in the list, should it be the other way around
> we could save a copy of the collection.
> (In my image (little more than trunk) there are only 2 senders of
>   polynomialEval:
> so maybe a change of semantics could be proposed to get rid of reverse...)
>
> Hope it helps
> Bye
> Enrico
>
> [1] Horner's rule/scheme http://en.wikipedia.org/wiki/Horner_scheme
>
>
> On Mon, Jul 25, 2011 at 11:21,  <commits at source.squeak.org> wrote:
>> Levente Uzonyi uploaded a new version of Collections to project The Trunk:
>> http://source.squeak.org/trunk/Collections-ul.450.mcz
>>
>> ==================== Summary ====================
>>
>> Name: Collections-ul.450
>> Author: ul
>> Time: 25 July 2011, 1:37:20.234 am
>> UUID: 2d09bd44-bfdf-1840-87cb-81ced69f9948
>> Ancestors: Collections-nice.449
>>
>> Avoid a multiplication, use low level methods in
>> SequenceableCollection >> #polynomialEval: for better performance.
>>
>> =============== Diff against Collections-nice.449 ===============
>>
>> Item was changed:
>>  ----- Method: SequenceableCollection>>polynomialEval: (in category 'enumerating') -----
>>  polynomialEval: thisX
>> -       | sum valToPower |
>>        "Treat myself as the coeficients of a polynomial in X.  Evaluate it with thisX.  First element is the constant and last is the coeficient for the highest power."
>>        "  #(1 2 3) polynomialEval: 2   "   "is 3*X^2 + 2*X + 1 with X = 2"
>>
>> +       | size sum valToPower |
>> +       sum := self at: 1.
>> +       (size := self size) = 1 ifTrue: [ ^sum ].
>> -       sum := self first.
>>        valToPower := thisX.
>> +       2 to: size - 1 do: [ :ind |
>> -       2 to: self size do: [:ind |
>>                sum := sum + ((self at: ind) * valToPower).
>> +               valToPower := valToPower * thisX ].
>> +       ^sum + ((self at: size) * valToPower)!
>> -               valToPower := valToPower * thisX].
>> -       ^ sum!
>>
>>
>>
>
>
>
> --
> Enrico Spinielli
> "Do Androids dream of electric sheep?"— Philip K. Dick
> "Hear and forget; see and remember;do and understand."—Mitchel Resnick
>



-- 
Enrico Spinielli
"Do Androids dream of electric sheep?"— Philip K. Dick
"Hear and forget; see and remember;do and understand."—Mitchel Resnick