[Jprogramming] Creating a matrix (some polish required)

[Richard Hill]

Alex,
At the risk of going off-topic it would be good to know how you solved the
multi-level problem using linear algebra in J.
(ie multi-level with common subassy)
A ref to the appropriate wiki or J phrase would be enough.


-----Original Message-----
From: programming-bounces at jsoftware.com
[mailto:programming-bounces at jsoftware.com] On Behalf Of Alex Rufon
Sent: Monday, 23 August 2010 12:10
To: Programming forum
Subject: Re: [Jprogramming] Creating a matrix (some polish required)

I remember identity matrix taught in my linear algebra class and wondering
how to use it in "real life" situation. 

Because of J, I actually used this concept to compute for Raw Material
Consumption and Material Requirement Planning for Shoes and Apparel
manufacturing (and soon for the Fishing Industry).  I remember doing RMC and
MRP in VB+PL/SQL when I was still working in the Paper Industry and the code
was mind boggling. I remember being confused where an IF-ENDIF block ends
because of the multi-leveling. Learning J to implement identity matrix and
matrix math is totally worth it. 

-----Original Message-----
From: programming-bounces at jsoftware.com
[mailto:programming-bounces at jsoftware.com] On Behalf Of Roger Hui
Sent: Friday, August 20, 2010 9:55 PM
To: Programming forum
Subject: Re: [Jprogramming] Creating a matrix (some polish required)

http://www.jsoftware.com/jwiki/Essays/Identity%20Matrix

34 ways to create the identity matrix.  Adapt one to create the
anti-diagonal matrix.  e.g. method 23:

   a23=: |.D.1 at i.
   a23 5
0 0 0 0 1
0 0 0 1 0
0 0 1 0 0
0 1 0 0 0
1 0 0 0 0



----- Original Message -----
From: Alex Gian <alexgian at blueyonder.co.uk>
Date: Friday, August 20, 2010 3:42
Subject: [Jprogramming] Creating a matrix (some polish required)
To: Programming forum <programming at jsoftware.com>

> The "flipped" identity matrix is quite interesting. (Basically it's 
> the identity matrix flipped or mirrored about either the vertical or 
> horizontal axis.  IOW, for a 3x3:
> 0 0 1
> 0 1 0
> 1 0 0
> I don't know if it has any special name, I stumbled on it by chance 
> while messing around with a simple FSA for a puzzle game.
> Pre-multiplying by this matrix flips any same size matrix vertically, 
> post-multiplying flips it horizontally.  Its square is obviously the 
> identity matrix.
> 
> Now, I have created this matrix on various systems, (e.g. HP/RPL, 
> Scheme, TI-Basic), usually - if an id matrix is provided - just by 
> reversing its rows, otherwise just by starting off with the vector, 
> say,
> 0 0 0 1, and then rotating the "1" each time and appending that vector 
> to a string, which is eventually converted to a matrix.
> 
> I can do this using loops and explicit coding, but am looking for any 
> suggestions to make it into a J one-liner, such that:
> flipidm 4
>   0 0 0 1
>   0 0 1 0
>   0 1 0 0
>   1 0 0 0
> 
> Hope my explanation was clear enough, TIA
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