Hi Martin
I think you're absolutely right about this;
One thing I need again and again is
a multinomial function, and usually define:
> lmultinomial
function (x)
{
lfactorial(sum(x)) - sum(lfactorial(x))
}
> multinomial
function (x)
{
exp(lmultinomial(x))
}
It would be nice to have this in base R.
Is this the place to discuss having complex
arguments for gamma()?
best wishes
rksh
Martin Maechler wrote:
lgamma(x) and lfactorial(x) are defined to return
ln|Gamma(x)| {= log(abs(gamma(x)))} or ln|Gamma(x+1)| respectively.
Unfortunately, we haven't chosen the analogous definition for
lchoose().
So, currently
> lchoose(1/2, 1:10)
[1] -0.6931472 -2.0794415 NaN -3.2425924 NaN -3.8869494
[7] NaN -4.3357508 NaN -4.6805913
Warning message:
In lchoose(n, k) : NaNs produced
>
which (the NaN's) is not particularly useful.
(I have use case where I really have to workaround those NaNs.)
I herebey propose to *amend* the definition of lchoose() such
that it behaves analogously to lgamma() and lfactorial(),
i.e., to return
log(abs(choose(.,.))
Your comments are welcome.
Martin Maechler, ETH Zurich
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