Re: [Rd] Bug in rt() ? (PR#9422)

From: <>
Date: Thu 21 Dec 2006 - 01:08:53 GMT

Hash: SHA1

Prof Brian Ripley wrote:
> Why do you consider this might be a bug in R rather than in your
> expectations? Your 'expected' is not what others have expected ....

Thank you for this response. I did consider at the time that this unexpected result could be deliberate, but help(rt) on 2.4.1 seemed to confirm my expectations. Martin Maechler noted on the first response to this bug report that help(rt) was not updated to describe the new functionality of rt().

> In 2.4.1 rt(ncp) operates continuously as ncp is varied through 0.
> That is different from saying that you want a central t (omitting ncp).

I was not expecting random draws from a central t distribution to be the same as random draws from a limiting case of a non-central t distribution. I was expecting that redundantly typing the default arguments of a function would produce the same result as omitting the default arguments. Are there other functions with this discrepancy?

In other words, I do not understand why rt() continues to default to ncp = 0, as opposed to no default argument for ncp. It would seem that args(rt) currently implies that the draws are to be taken from a limiting case of non-central t distribution, when this is not accurate if the ncp argument is omitted.


Version: GnuPG v1.4.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla -

iD8DBQFFid58zQDSXIcN85kRAhRVAJ0WNf2fMVcPZk4rfxw8qXO272Bs8ACfdVAt a5OaqyObzqkjL8a5sCooj6w=
-----END PGP SIGNATURE----- mailing list Received on Thu Dec 21 18:34:46 2006

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Thu 21 Dec 2006 - 08:31:03 GMT.

Mailing list information is available at Please read the posting guide before posting to the list.