Correspondence

Transcribed from the printed issue; not yet reviewed. Read it in the PDF of the issue, page 9

Vol 18.1 : "Vector is a fun game … "¶

From: Ajay Askoolum, 16th October 2001

From 18.1, I read that ‘Vector is thriving; it has more material available than usual.’ in the Minutes of the AGM and ".. we are lacking a bit APL contributions.." in the Editor’s reply. What am I to believe?

Vector will not last beyond 10 years if it is depleting its asset to the order of roughly £4000 per year, year on year.

Sincere congratulations to the ‘Outstanding Achievement Award’ winner – APL on the .Net platform keeps APL in the news and that is good news for APL. But, who were the other nominees?

Yet one more published letter on the issue of what appears in Vector! Mercifully, this time it was not about J, albeit more pages continue to carry J than APL, but about the relevance of articles. I subscribe to Vector because I want to read about APL, nothing else. If I can do that, the revised annual subscription cost is not a problem. I can read about other things elsewhere but about APL nowhere else.

Inversion of Binary Matrices¶

From: Mike Day, 7th October 2001

Michel Dumontier writes about Inversion of Binary Matrices.

I’d just like to point out that I included a binary inversion function in my article about solving a puzzle:

Day, Mike The MAGIC Goes Away – Opening the Boxes Vol 10.1, 125

It wasn’t particularly original; I’d adapted one of Keith Smillie’s Statpack functions.

My introductory comments state:

⍝  INVERT A SQUARE BINARY MATRIX... AFTER KW SMILLIE'S STATPACK
2⍝  NB REAL ADD/MINUS BOTH BECOME ≠
⍝     REAL TIMES BECOMES ×
⍝     REAL ÷ SHOULDN'T BE NECESSARY AS DIVISOR IS 0 OR 1
⍝
⍝  AN ALTERNATIVE METHOD IS TO TAKE
⍝       2 | (DETERMINANT A) × ⍙A
⍝  BUT THAT NEEDS A DETERMINANT FUNCTION OF SIMILAR COMPLEXITY
⍝               TO THIS ONE

I recall that the late Gérard Langlet also wrote in Vector about the puzzle.