product of empty vectors

[John W. Eaton]

On 23-May-2003, Douglas Harder <address@hidden> wrote:

| Octave's handling of empty matrices is a little odd:
| 
| >> a = 1:2 
| a =
|   1  2
| >> a(1:0)
| ans = []
| >> ans * ans'   % this should be 0
| ans = []
| >> ans + 3
| ans = []

The only real problem here is that Octave interprets 1:0 as a 0x0
empty matrix instead of a 1x0 empty matrix.  Should we change that?

If you actually generate a 1x0 matrix, the rest works as you expect:

  octave:1> x = zeros (1,0)
  x = [](1x0)
  octave:2> x*x'
  ans = 0

Likewise, the indexing works as you expect:

  octave:3> a = 1:2
  a =

    1  2

  octave:4> a(x)
  ans = [](1x0)

and of course 0+3 == 3.

| Hopefully this wasn't a design decision in Octave to convert all
| empty matrices to 0x0. 

No.  In fact, Octave had empty matrices with nonzero dimensions before
Matlab.

jwe



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