On 15 September 2011 10:08, Juan Pablo Carbajal <[email protected]> wrote:
> Dear all,
>
> I have added to the features tracker a small set of functions that I
> think they could go into the specfun package.
>
> https://sourceforge.net/tracker/?func=detail&aid=3409993&group_id=2888&atid=352888
>
Below is a much better implementation of multinom_exp, which uses the
standard stars and bars method for counting monomials, or in this
case, enumerating them:
function alpha = multinom_exp(m, n)
## This is standard stars and bars.
numsymbols = m+n-1;
stars = nchoosek(1:numsymbols, n);
## Star labels minus their consecutive position becomes their index
## position!
idx = bsxfun(@minus, stars, [0:n-1]);
## Manipulate indices into the proper shape for accumarray.
nr = rows(idx);
idx = [repmat([1:nr], n,1)(:), idx'(:)];
alpha = accumarray (idx, ones(nr*n, 1));
endfunction
HTH,
- Jordi G. H.
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