Re: Class of User Types [Was: Moving code from octave-forge to octave [Was: polyderiv problem?]]

[Paul Kienzle]

On Feb 25, 2005, at 8:24 AM, David Bateman wrote:

> Paul Kienzle wrote:
> > Another alternative is to delay recording the primitive polynomial 
> > type
> > until something is actually assigned to the matrix, and from then on 
> > check
> > that it is consistent.  Would that work for you?
> Err, I have to admit that you can do
>
> gf(floor(8*rand(4,4)),8) + ones(4,4)
>
> As the galois/matrix operations are already taken into account with 
> the matrix promoted the a galois field. However
>
> a = zeros(4,4); a(:,1) = gf(floor(8*rand(4,1)),8)
>
> won't promote a, but leave it as a matrix, and so the implementation 
> of triu won't work. I suppose an alternative for the galois fields is 
> to modify the assign function to promote the matrix to a galois field 
> as well... This might also work for the fixed point operators.

I was thinking:

   z = zeros(4,4,class(X));
   for i=1:columns(X), z(1:i,:) = X(1:i,:); end

so z would already be known to be a galois type but with an 
indeterminate
field.

> > Or maybe something more generic, such as array(exemplar,dims) so that
> > dispatch will work.  Also, this makes more sense for some types such
> > as 'cell' for which I was assuming the zeros function would create a
> > set of empty cells.
> >
> > Then triu would be:
> >
> >    z = array(X,size(X));
> >    for i=1:columns(X), z(1:i,:) = X(1:i,:); end
> >
> >
> > Otherwise, zeros(dims,'auto',exemplar) does do what we want assuming
> > the class registers a zeros constructor.
> I don't see that we need an explicit zero constructor,
>
> octave_value retval = args(0);
> retval = retval.resize(dim_vector(0,0)).resize(args(0).dims());
>
> does exactly the right.

Okay, that means we can implement it without touching octave.  I'm
not too keen on the name 'array' though.  I suppose we could get
away with just exposing resize and implement triu as:

    z = resize(resize(X,[0,0]),size(X));
    for i=1:columns(X), z(1:i,:) = X(1:i,:); end

Not quite as pretty but it'll do.  Resize can also be used to implement
postpad.


- Paul