Change to vander.m

[John W. Eaton]

On 15-Jan-2008, Thomas Weber wrote:

| I'd like to propose the attached patch to vander.m.
| 
| Advantage: it's faster for large arguments (a vector size of 3 has a
| comparable speed).
| 
| Disadvantages: slower for length(c) == 2 and it needs more memory
| (although if the memory needs start to be a problem, the for-loop in the
| current implementation will hit even harder).
| 
|       Thomas
| ? plot/.hg
| Index: special-matrix/vander.m
| ===================================================================
| RCS file: /cvs/octave/scripts/special-matrix/vander.m,v
| retrieving revision 1.25
| diff -u -r1.25 vander.m
| --- special-matrix/vander.m   12 Oct 2007 21:27:26 -0000      1.25
| +++ special-matrix/vander.m   15 Jan 2008 20:23:18 -0000
| @@ -58,13 +58,17 @@
|  
|    if (isvector (c))
|      n = length (c);
| -    retval = zeros (n, n);
| -    j = 1:n;
| -    for i = 1:n
| -      retval(i,:) = c(i) .^ (n - j);
| -    endfor
| +    N = ones(n,1) * [n-1:-1:0];
| +    C = c(:) * ones(1,n);
| +    retval = C .^ N;

Is there any need for the variables N and C?  why not just write

  retval = (c(:) * ones (1, n)) .^ (ones (n, 1) * (n-1:-1:0));

?

I made this change.

Thanks,

jwe