[Jprogramming] Simple scalar multiplication of matrices

['Jon Hough' via Programming]

Thanks for the responses. It seems ravelling the left argument is the easiest way to go.


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On Tue, 4/19/16, 'Pascal Jasmin' via Programming <programming at jsoftware.com> wrote:

 Subject: Re: [Jprogramming] Simple scalar multiplication of matrices
 To: "programming at jsoftware.com" <programming at jsoftware.com>
 Date: Tuesday, April 19, 2016, 8:28 AM
 
 there is also the adverb
 (no source transforms)
 
  (i.
 1 4) *"1 1"1 2 i. 2 4
 0 1  4 
 9
 0 5 12 21
 
 
 (or shorthand)
 
 "1"1 2
 
 
 
 ----- Original Message -----
 From: EelVex <eelvex at gmail.com>
 To: Programming forum <programming at jsoftware.com>
 Sent: Monday, April 18, 2016 4:49 AM
 Subject: Re: [Jprogramming] Simple scalar
 multiplication of matrices
 
 If you remove the first axis of a you can
 multiply-1:
 
 (,a) *"1
 b
 10 22 36 52
 14 30 48 68
 
 Do you really need a to be 1xn
 ?
 
 
 On Mon,
 Apr 18, 2016 at 11:41 AM, 'Jon Hough' via
 Programming <
 programming at jsoftware.com>
 wrote:
 
 > I am sure there
 is a simple answer to this, but I would like to know it.
 >
 > Say I have two
 matrices:
 >
 > a =: 1 4
 $ 1 2 3 4
 > b =: 2 4 $ 10 11 12 13 14 15
 16 17
 >
 > and I want
 to multiply a's single row element-wise with each of
 b's rows.
 > Not matrix
 multiplication, so the resulting matrix should have
 dimensions 2
 > 4, same as b.
 >
 > Obviously a * b gives
 a length error,
 >
 > So
 does a *"1 1 b
 >
 > My best solution is pretty ugly,
 >
 > (($b)$,a ) * b
 >
 > i.e. reshape a so it
 has the same number of rows as b, which duplicates
 > the items of its top row into the second
 row and then multiply row-wise.
 >
 > Is there a better way?
 > Incidentally, isn't a*1 1 b a
 row-to-row multiplication. I thought this
 > would have worked, and am slightly
 confused why it doesn't.
 >
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