Or, slightly more efficient (if that matters):
V1=: |:(2 3 4;2.3),(1 2;3.9),: 2 3 4;3.1
V2=: (~.@{.,:+/&.:>/./)V1
V2-:|:(2 3 4;5.4),: 1 2;3.9
(Caution: email clients have become hostile to copy&paste, and may not
represent code accurately.)
Thanks,
--
Raul
On Mon, Nov 25, 2019 at 1:11 PM Raul Miller <[email protected]> wrote:
>
> Your approach is exactly what my f does!
>
> That said, there's other ways of phrasing this. Also, for this
> specific calculation, it would be easier to work with a representation
> of the form
> V1=: |:|.@> v1
> V2=: |:|.@> v2
>
> Then:
> V2-:(~.@{.,:+&.>//./)V1
> 1
>
> It may help to use the dissect utility documented at
> https://code.jsoftware.com/wiki/Vocabulary/Dissect or to inspect the
> results of sub-expressions.
>
> (Mostly, when working with J -- and, for that matter, other languages
> -- I find it pays to focus on how the data looks as it's being
> transformed instead of trying to focus on the code itself. The code is
> obvious and in front of you, but the intermediate results are harder
> to see...)
>
> Thanks,
>
> --
> Raul
>
> On Mon, Nov 25, 2019 at 12:24 PM Arnab Chakraborty <[email protected]> wrote:
> >
> > Thanks, Raul. You are always so prompt with your help! I am yet to decipher
> > your solution, but your suggestion regarding 2 column table is bang on
> > point.
> >
> > My own approach was something like this: find nub of the 2nd column, then
> > for each element in the nub collect all occurences of it, and sum over the
> > coeffns.
> >
> > On Mon, 25 Nov 2019, 21:56 Raul Miller, <[email protected]> wrote:
> >
> > > Yes, definitely.
> > >
> > > For example, consider:
> > >
> > > <"1 ({:"1 (+&.>/@:({."1), (<0 1){])/. ])>v1
> > >
> > > Or,
> > >
> > > f=: 13 :'<"1 ({:"1 (+&.>/@:({."1), (<0 1){])/. ])>y'
> > > f v1
> > >
> > > That said, this example may fall apart for your general case? (I don't
> > > know what that is...)
> > >
> > > Specifically, I don't know why the top level structure of v1 and v2
> > > would be a list of boxed entities if they are always pairs. It seems
> > > to me that a table of two columns would be a more natural expression
> > > of that, if that's the case.
> > >
> > > Thanks,
> > >
> > > --
> > > Raul
> > >
> > >
> > > On Mon, Nov 25, 2019 at 11:12 AM Arnab Chakraborty <[email protected]>
> > > wrote:
> > > >
> > > > Dear all,
> > > >
> > > > I am trying to implement a geometric algebra system in J. I have done
> > > > much of the stuff, but is getting stuck at one point. Hence this email.
> > > >
> > > > Basically, I have a list of boxes like
> > > >
> > > > v1=: (<2.3; 2 3 4), (<3.9; 1 2), <3.1; 2 3 4
> > > >
> > > > This represents a (multi)vector whose math representation is
> > > >
> > > > 2.3 * e_{234} + 3.9 * e_{12} + 3.1 * e_{234}.
> > > >
> > > > Here the e_{...}'s are some basis vectors. As you can see, e_{234}
> > > > occurs
> > > > twice in the list, and so this vector may be reduced to
> > > >
> > > > 5.4 * e_{234} + 3.9 * e_{12}.
> > > >
> > > > In J this should be
> > > >
> > > > v2=:(<5.4; 2 3 4), <3.9; 1 2
> > > >
> > > > I want to write a monad f such that f v1 is v2.
> > > >
> > > > Any idea?
> > > >
> > > > Thanks and regards.
> > > >
> > > > Arnab.
> > > > ----------------------------------------------------------------------
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> > > ----------------------------------------------------------------------
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> > >
> > ----------------------------------------------------------------------
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