[S] uniroot -- doesn't work recursively

) However, note that R currently has the same problem as S-plus:

) Uniroot() doesn't work reliably, recursively.
) When you found it to be better, you were just lucky.

Right.  I realised later on that R seemed to behave better but 
it could not work properly since it calls a Fortran (66? 77?) routine.
It just happen to produce less obviously wrong answers than Splus.
In fact more tests confirm wrong answers, but not as non-sensical 
as those from Splus.

To get around the problem,  I have replaced  f(x)=0 by f^2(x)=min,
where f(x)is computed with the aid of uniroot(), and the minimization
is solved by optimize(). This works.

Martin Maechler <maechler@stat.math.ethz.ch> writes:


Well, uniroot calls zeroin which is a FORTRAN routine. As long as this
is the case, all bets are off as to whether or not it will be
reentrant on any given system. In principle, it is not, and FORTRAN
just plain states that "you cannot do that", but if your compiler
happens to be f2c-like, and no global storage is involved, then it
*might* work after all. The example doesn't work on my system either.

The only sensible thing to do to get this to work is to rewite zeroin
in C. According to the comments in the file, it is a transcription of
an Algol60 program, so it is probably not hard to convert it to
another Algol descendant.

My R 0.64 is obtained from the binary file distributed by CRAN in Wien
(compiled by Guido Masarotto?), so I do not know which the compiler is 
used.

Thanks for your comments

Regards
Adelchi Azzalini
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