I'm not as conversant with rank as you are. To my way of thinking,
you want to multiply each row of "a" by each row of the multiplier:
a *"1/2 4$ 1 1 0 0 0 0 1 1
1 1 0 0
0 0 1 1
1 1 0 0
0 0 2 2
1 1 0 0
0 0 3 3
1 1 0 0
0 0 4 4
This gives a 3-D result, which may be handy depending on what you next
plan to do with this. However, as David shows, you can also ravel the
first two dimensions into one:
,/a *"1/2 4$ 1 1 0 0 0 0 1 1
1 1 0 0
0 0 1 1
1 1 0 0
0 0 2 2
1 1 0 0
0 0 3 3
1 1 0 0
0 0 4 4
On Wed, Sep 5, 2012 at 9:56 PM, David Ward Lambert
<b49p23t...@stny.rr.com> wrote:
> Right! "Matrix multiplication" usually means something else.
> You want a sort of element-by-corresponding-element multiplication.
>
> B ; A
> +-------+-------+
> |1 1 0 0|1 1 1 1|
> |0 0 1 1|1 1 2 2|
> | |1 1 3 3|
> | |1 1 4 4|
> +-------+-------+
>
> A solution uses rank conjunction twice. I couldn't begin to understand
> it the first time I saw this sort of construction. Then one day I wrote
> rank rank and retrospectively realized what I'd written and understood.
> I practiced rank with sentences like 'abc' "2 i. 2 3 4
>
> My thoughts to construct this sentence:
> First I realized that you need to multiply row by row.
> The ("1) adverb ensures this. The frames of these two matrices disagree
> because there are 2 rows in B and 4 in A. The next adverb ("_ 1) means
> (because ultimately the final verb is dyadic) "use all of the left array
> with each row of the right hand array".
>
> B * ("1) ("_ 1) A
> 1 1 0 0
> 0 0 1 1
>
> 1 1 0 0
> 0 0 2 2
>
> 1 1 0 0
> 0 0 3 3
>
> 1 1 0 0
> 0 0 4 4
>
> Finally, inserting append between the pages gives
>
> ,/B*"1"_ 1 A
> 1 1 0 0
> 0 0 1 1
> 1 1 0 0
> 0 0 2 2
> 1 1 0 0
> 0 0 3 3
> 1 1 0 0
> 0 0 4 4
>
>
> ----------------------------------------------------------------------
> 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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