overloading functions (Was: Indirect Addressing Question)

[adler]

On Wed, 14 Nov 2001, Paul Kienzle wrote:
> Andy, is there is sparse sum function?

I've just uploaded spsum.m to octave-forge.

It should be pretty fast as an *.m file - but I may
get around to doing it in *.cc later.

In the meantime, I have a question/bug report

For column vectors, the direction parameter of sum
allows control of the direction

   octave-2.1.34:37> sum( [1 2 3]' )
   ans = 6
   octave-2.1.34:38> sum( [1 2 3]',1 )
   ans = 6
   octave-2.1.34:39> sum( [1 2 3]',2 )
   ans =
     1
     2
     3

However, this is not the case for row vectors.

   octave-2.1.34:34> sum( [1 2 3] )
   ans = 6
   octave-2.1.34:35> sum( [1 2 3],1 )
   ans = 6
   octave-2.1.34:36> sum( [1 2 3],2 )
   ans = 6

In other words sum(x) == sum(x,1).

Is this a bug?



> Anyone want to take a shot at modifying the interpreter so that you can
> overload functions for user-defined types?

This would be a _good thing_.

My suspicion is that this would be hard. You really need
quite a lot of OO infrastructure to this king of
function overloading. Matlab syntax and semantics don't
support this king of stuff.

I would really like this feature though, maybe someone can
think of a way to make it work.

> An alternative would be to replace the builtin function sum with a new one
> from sparse/sum.cc which tests if the type is sparse and if not calls
> the builtin sum function, but Octave won't support that either.  Besides,
> it is even ickier.

I've just added is_sparse, is_real_sparse, is_complex_sparse
for anyone who wants to try something like this.

_______________________________________
Andy Adler,                address@hidden





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