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 <d...@shaw.ca> 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.
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>>
>>
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>
--
Devon McCormick, CFA
^me^ at acm.
org is my
preferred e-mail
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