Here's what I get for timings for some of these methods:
NB. Various ways to create ] x ] identity mat.
idMat0=: =@:i.
idMat1=: 3 : '(2$y)$(>:y){.1' NB.* faster, scales better
idMat2=: ,~ $ >: {. 1:
(10) 6!:2 'idMat0 &.> 36000 38000 40000 42000 44000 46000 48000 50000'
21.7756
(10) 6!:2 'idMat1 &.> 36000 38000 40000 42000 44000 46000 48000 50000'
9.55495
(10) 6!:2 'idMat2 &.> 36000 38000 40000 42000 44000 46000 48000 50000'
23.0792
If you need a *:5e4 identity matrix, you're in trouble.
On Tue, Nov 20, 2012 at 6:04 PM, bob therriault <[email protected]>wrote:
> Devon,
>
> I like that, or another tacit option
>
> idMat1=: ,~ $ >: {. 1:
> idMat1 6
> 1 0 0 0 0 0
> 0 1 0 0 0 0
> 0 0 1 0 0 0
> 0 0 0 1 0 0
> 0 0 0 0 1 0
> 0 0 0 0 0 1
>
> Cheers, bob
>
> On 2012-11-20, at 1:33 PM, Devon McCormick wrote:
>
> > I used to have a named verb "idMat" in my own utilities library that was
> > defined this way:
> > idMat=: =@:i.
> >
> > but testing this on large arguments led me to formulate this
> > idMat=: 3 : '(2$y)$(>:y){.1' NB.* faster and scales better
> >
> > or, the same thing tacitly:
> > idMat=: (2 $ ]) $ 1 {.~ >:
> >
> >
> > On Tue, Nov 20, 2012 at 2:29 PM, Don & Cathy Kelly <[email protected]> wrote:
> >
> >> A key point that dawned on me, after reading all the helpful comments
> and
> >> suggestions that have come in, is that I don't need a verb- just a noun
> - so
> >> y=: 2 3 4 2 2 3 (it also works for an n,n array)
> >>
> >> ] u=:=i.# y
> >>
> >> 1 0 0 0 0 0
> >> 0 1 0 0 0 0
> >> 0 0 1 0 0 0
> >> 0 0 0 1 0 0
> >> 0 0 0 0 1 0
> >> 0 0 0 0 0 1
> >>
> >> and I can use u*y for different 'y''s ( as long as the # is the
> same)
> >> to get the desired diagonal elements with off diagonal elements 0
> >> I want this because I want to add to the diagonal elements of a matrix.
> >> This is for a Newton Raphson based power system load flow.
> >>
> >> Thanks to all,
> >> Don
> >>
> >>
> >>
> >> On 20/11/2012 8:24 AM, Roger Hui wrote:
> >>
> >>> http://www.jsoftware.com/**jwiki/Essays/Identity%20Matrix<
> http://www.jsoftware.com/jwiki/Essays/Identity%20Matrix>: 34 different
> ways
> >>> to generate the identity matrix of order n; the first is =@i. and the
> last
> >>> is _&q:@p:@i.
> >>> ------------------------------**------------------------------**
> >>> ----------
> >>> For information about J forums see
> http://www.jsoftware.com/**forums.htm<http://www.jsoftware.com/forums.htm>
> >>>
> >>>
> >>
> ------------------------------**------------------------------**----------
> >> For information about J forums see
> http://www.jsoftware.com/**forums.htm<http://www.jsoftware.com/forums.htm>
> >>
> >
> >
> >
> > --
> > Devon McCormick, CFA
> > ^me^ at acm.
> > org is my
> > preferred e-mail
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
>
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
--
Devon McCormick, CFA
^me^ at acm.
org is my
preferred e-mail
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