[Jprogramming] J FAQ

[Yuvaraj Athur Raghuvir]

Believe me, thats what I have been doing for the past couple of hours!!
JfC : 5 & 6
LJ : 7
and lots of other reading....

It helps newbies to hit the books and read about ranks, cells and frames
when trying to decipher the matrix multiplication. A reference to this in
the FAQ might help.

Thanks!


On 10/1/06, Henry Rich <HenryHRich at nc.rr.com> wrote:
>
> May I suggest chapters 5 and 6 of _J for C Programmers_
> (available in J6 by F1, then JfC)
>
> Henry Rich
>
> > -----Original Message-----
> > From: programming-bounces at jsoftware.com
> > [mailto:programming-bounces at jsoftware.com] On Behalf Of
> > Yuvaraj Athur Raghuvir
> > Sent: Sunday, October 01, 2006 2:08 PM
> > To: Programming forum
> > Subject: Re: [Jprogramming] J FAQ
> >
> > I am still struggling with ranks, cells and frames. Thanks
> > for the pointers.
> >
> >
> >
> >
> > On 10/1/06, Miller, Raul D <rdmiller at usatoday.com> wrote:
> > >
> > > Yuvaraj Athur Raghuvir wrote:
> > > > u . v is defined by u@(v"(1+lv,_)) , ...
> > > ...
> > > > Q1. What does the part "1+lv" mean?
> > >
> > > It's part of v"(1+lv,_)
> > >
> > > This is an expression involving rank.  See also
> > > http://www.jsoftware.com/help/dictionary/intro20.htm
> > > http://www.jsoftware.com/help/dictionary/d600v.htm
> > >
> > > > I assume lv means rank of * which the dictionary states is 0 0 0 .
> > >
> > > Actually, lv is the left rank of v, which is the middle element
> > > of that vector.  The three numbers are: monad rank,
> > > left rank, right rank.
> > >
> > > > Q2.  There is a third 0 in the rank definition of *. That is being
> > > ignored.
> > > > Why?
> > >
> > > Because the monad definition of * is not being used here.
> > >
> > > >  This gives me:
> > >
> > > > Q3. But how does J pick the column of B here as the cells
> > to which to
> > > apply
> > > > "*"? Can this be illustrated with appropriate J command
> > to display the
> > > > columns of B that would be consumed when * is applied?
> > >
> > > Here is an expression which uses that rank with a different verb:
> > >
> > >   A ;"1 _ B
> > >
> > > I hope this helps.
> > >
> > > --
> > > Raul
> > >
> > >
> > >
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