[Jprogramming] Spare Matrix from Index Matrix

[Roger Hui]

4$.s is not invertible.



----- Original Message -----
From: ramacd <ramacd at nbnet.nb.ca>
Date: Saturday, February 3, 2007 6:07 am
Subject: Re: [Jprogramming] Spare Matrix from Index Matrix

> It seems Roger is a mortal;
> 
>   s=: ?4 4$2
>   (4&$.)^:_1 (4 $. s)
> |domain error
>   (4&$.)^:_1(4 $.s)
> 
> ...or is my copy of J too old?