Re: [Bug-apl] Domino Domain

[Juergen Sauermann]

Hi Mike,

thanks. Maybe fixed in SVN 667. I am now using ⎕CT (instead of a fixed constant 1E¯10) as
the condition number in ⌹. This number determines if a matrix is considered singular or not.

Neither the ISO standard nor the IBM APL2 manual says anything about that aspect, so I hope
it is OK now.

/// Jürgen

On 08/25/2015 08:30 PM, Mike Duvos wrote:

GNU APL's domino gives a domain error for matrices that are close to singular, but aren't.

      )clear
CLEAR WS

      A←100 100⍴101↑1
      A[1;1]←0

[IBM APL2]

       10 10 ↑⌹A+⎕CT×100
 1.000000001E11 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1 ¯1
¯1.000000000E0   1  0  0  0  0  0  0  0  0
¯1.000000000E0   0  1  0  0  0  0  0  0  0
¯1.000000000E0   0  0  1  0  0  0  0  0  0
¯1.000000000E0   0  0  0  1  0  0  0  0  0
¯1.000000000E0   0  0  0  0  1  0  0  0  0
¯1.000000000E0   0  0  0  0  0  1  0  0  0
¯1.000000000E0   0  0  0  0  0  0  1  0  0
¯1.000000000E0   0  0  0  0  0  0  0  1  0
¯1.000000000E0   0  0  0  0  0  0  0  0  1

[GNU APL]

      10 10 ↑⌹A+⎕CT×100
DOMAIN ERROR
      10 10↑⌹A+⎕CT×100
            ^^

A matrix whose determinant is 1E¯11 is obviously not singular.