Using diagonal matrix as index

[Søren Hauberg]

fre, 09 01 2009 kl. 16:47 -0500, skrev John W. Eaton:
> On  9-Jan-2009, Søren Hauberg wrote:
> 
> |   With a recent checkout I get the following IMHO quite odd behaviour:
> | 
> | octave:18> A = magic (5)
> | A =
> | 
> |    17   24    1    8   15
> |    23    5    7   14   16
> |     4    6   13   20   22
> |    10   12   19   21    3
> |    11   18   25    2    9
> | 
> | octave:19> A (diag (true (1, 4))) = 4
> | A =
> | 
> |     4    4    4    4   15
> |    23    5    7   14   16
> |     4    6   13   20   22
> |    10   12   19   21    3
> |    11   18   25    2    9
> | 
> | Shouldn't this have produced an error since I'm using a 4x4 matrix as
> | index in a 5x5 matrix? Also, why are the elements placed in first row,
> | instead of along the diagonal?
> 
> It's the same as if you had done
> 
>   A(find (diag (true (1, 4)))) = 4
> 
> If we change this behavior, then people will likely complain when they
> try to run the code they wrote for the other leading brand in Octave.
> So if you think it is a bug, complain to those other guys.

Ohh, I see. I thought it would be the same as

  A (full (diag (true (1, 4)))) = 4

which produces an error with the current code. So, I guess the bug is
that 'full' changes the class of diagonal matrices into 'double':

  octave:28> class (diag (true (1, 4)))
  ans = logical
  octave:29> class (full (diag (true (1, 4))))
  ans = double

I would assume that the latter should have produced 'logical'.

Søren



> 
> jwe