Ouch! I'm sorry for incomplete specification, the full one is very very
complex. I wasn't expecting to see a full solution. Ok, I'll try to
simplify specification before starting to solve a problem. Anyway I got the
point and this reply is really helpful, thank you again.
On Sun, Apr 5, 2015 at 5:01 PM, Raul Miller <rauldmil...@gmail.com> wrote:
> Why do you have recursive functions?
>
> Note that numbers themselves are recursive - most practical
> applications that "need recursive functions" can be redefined to
> instead "need functions with numeric domains".
>
> Put differently: a specification which specifies *how* something gets
> done will often be miserable to implement and have miserable
> performance. A specification which instead specified *what* needs to
> get done will tend to be more pleasant to work with.
>
> Translating between them tends to be a "mere matter of mathematics"
> (which, ok, is sometimes intractable).
>
> But impractical problems can be a sign that you should avoid J and
> instead work with the language the problems were designed for.
>
> That said, I'd just code it up in the simplest most obvious way and
> then take a look at what the results were like to decide if I wanted
> to do anything different.
>
> That said, in the case of:
>
> F(t,i,j,k) is a minimum of
> {C(i,j,k)+ sum of all g(t-1, i',j',k) + sum of all h(t-1, i, j", k') }
> and
> {F(t,i-1,j,k-1)+1},
> where C -- user defined cost function,
> i' from 0 to i-1, j' and j" from zero to j-1, k' from 0 to k-j.
>
> That's an incomplete specification.
>
> It's not just that you've not defined C, g and h, but you've also not
> specified what F is like when you have zeros for either of the even
> numbered arguments. (Also, you seem to have an implicit constraint
> that k be no smaller than j -- but at least that's sort of stated.)
>
> I also think it's a mistake to declare j' and j'' as being independent
> - I don't see any valid reason for that. At least, not yet.
>
> In other words, a quick and dirty implementation might look like this:
>
> F=:3 :0
> 't i j k'=. y
> I=. i.i assert. i>:0
> J=. i.j assert. j>:0
> K=. i.1+k-j assert. k>:j
> G=.+/,g&> (t-1),each ({I;J),each k
> H=.+/,h&> (t-1),each i,each {J;K
> (1+F t;(i-1);j;k-1) <. (C i;j;k)+G+H
> )
>
> And that will always fail. Do you see why?
>
> Anyways... the general rule is: first make sure you are computing the
> right result - that you are solving the right problem. It's not worth
> bothering to trying to do anything else until you've gotten past that
> point.
>
> Once you have a sample solution (and that includes having reasonably
> sized example data and corresponding example results) it's often worth
> spending some time trying to understand what's happening so you can do
> it better.
>
> Thanks,
>
> --
> Raul
>
>
>
> --
> Raul
>
> On Sun, Apr 5, 2015 at 5:34 AM, Sergeif <ifse...@gmail.com> wrote:
> > I'm not sure. May be I should use memoization instead. I have a bunch of
> > recursive functions f,g,h,... defined like this:
> >
> > F(t,i,j,k) is a minimum of
> > {C(i,j,k)+ sum of all g(t-1, i',j',k) + sum of all h(t-1, i, j", k') }
> > and
> > {F(t,i-1,j,k-1)+1},
> > where C -- user defined cost function,
> > i' from 0 to i-1, j' and j" from zero to j-1, k' from 0 to k-j.
> >
> > I'm intrested in a value of F(T,N,M,K) for some T,N,M,K ≤ 1000. A common
> > pattern for tasks like this would be very helpful for me.
> > 04 апр. 2015 г. 23:50 пользователь "Henry Rich" <henryhr...@nc.rr.com>
> > написал:
> >
> >> It's unusual in J to need the full odometer array. Are you sure that
> your
> >> problem requires it?
> >>
> >> Henry rich
> >>
> >> On 4/4/2015 5:48 PM, Sergeif wrote:
> >>
> >>> Thanks! It's 10x faster than my code but 10x slower than odometer
> >>> function.
> >>> Anyway I lernt the catalogue verb from this.
> >>>
> >>> On Sat, Apr 4, 2015 at 11:21 PM, R.E. Boss <r.e.b...@outlook.com>
> wrote:
> >>>
> >>>
> >>>> >,{<@i."0[2 3 4
> >>>> 0 0 0
> >>>> 0 0 1
> >>>> 0 0 2
> >>>> 0 0 3
> >>>> 0 1 0
> >>>> 0 1 1
> >>>> 0 1 2
> >>>> 0 1 3
> >>>> 0 2 0
> >>>> 0 2 1
> >>>> 0 2 2
> >>>> 0 2 3
> >>>> 1 0 0
> >>>> 1 0 1
> >>>> 1 0 2
> >>>> 1 0 3
> >>>> 1 1 0
> >>>> 1 1 1
> >>>> 1 1 2
> >>>> 1 1 3
> >>>> 1 2 0
> >>>> 1 2 1
> >>>> 1 2 2
> >>>> 1 2 3
> >>>>
> >>>> R.E. Boss
> >>>>
> >>>>
> >>>> -----Original Message-----
> >>>>> From: programming-boun...@forums.jsoftware.com [mailto:programming-
> >>>>> boun...@forums.jsoftware.com] On Behalf Of Nollaig MacKenzie
> >>>>> Sent: zaterdag 4 april 2015 23:16
> >>>>> To: programm...@jsoftware.com
> >>>>> Subject: Re: [Jprogramming] indexing a table
> >>>>>
> >>>>> Is something like this what you have in mind?
> >>>>>
> >>>>> m=. i. 2 3 4
> >>>>> indmak m
> >>>>> 0 0 0
> >>>>> 0 0 1
> >>>>> 0 0 2
> >>>>> 0 0 3
> >>>>>
> >>>>> 0 1 0
> >>>>> 0 1 1
> >>>>> 0 1 2
> >>>>> 0 1 3
> >>>>>
> >>>>> 0 2 0
> >>>>> 0 2 1
> >>>>> 0 2 2
> >>>>> 0 2 3
> >>>>>
> >>>>>
> >>>>> 1 0 0
> >>>>> 1 0 1
> >>>>> 1 0 2
> >>>>> 1 0 3
> >>>>>
> >>>>> 1 1 0
> >>>>> 1 1 1
> >>>>> 1 1 2
> >>>>> 1 1 3
> >>>>>
> >>>>> 1 2 0
> >>>>> 1 2 1
> >>>>> 1 2 2
> >>>>> 1 2 3
> >>>>> indmak
> >>>>> (#: i.)@$
> >>>>>
> >>>>>
> >>>>> On 2015.04.04 23:09:58, you,
> >>>>> the extraordinary Sergeif, spake thus:
> >>>>>
> >>>>> Hi.
> >>>>>>
> >>>>>> How can someone create list of indexes of 3d table (N x M x K)?
> >>>>>>
> >>>>>> I have written this simple code:
> >>>>>>
> >>>>>> ind3d =: 3 : 0
> >>>>>> 'n m k' =. y
> >>>>>> p0 =. k&|
> >>>>>> p1 =. (m&|)@:<.@:(%&k)
> >>>>>> p2 =. <.@:(%&(m*k))
> >>>>>> (p2 , p1 , p0)"0 (i. (n*m*k))
> >>>>>> )
> >>>>>>
> >>>>>> but it's very very slow. Does any tacit solution for this problem
> >>>>>>
> >>>>> exist?
> >>>>
> >>>>>
> >>>>>> Another question is how to fill the table with values depending on
> >>>>>>
> >>>>> indexes
> >>>>
> >>>>> of cell? For example, F[i,j,k] = (i * j) - (i * k) + (j * k).
> >>>>>>
> ----------------------------------------------------------------------
> >>>>>> For information about J forums see
> >>>>>>
> >>>>> http://www.jsoftware.com/forums.htm
> >>>>>
> >>>>> --
> >>>>> Nollaig MacKenzie
> >>>>> http://www.yorku.ca/nollaig
> >>>>>
> ----------------------------------------------------------------------
> >>>>> For information about J forums see
> http://www.jsoftware.com/forums.htm
> >>>>>
> >>>> ----------------------------------------------------------------------
> >>>> For information about J forums see
> http://www.jsoftware.com/forums.htm
> >>>>
> >>>>
> ----------------------------------------------------------------------
> >>> For information about J forums see http://www.jsoftware.com/forums.htm
> >>>
> >>> ----------------------------------------------------------------------
> >> For information about J forums see http://www.jsoftware.com/forums.htm
> >>
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
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