[R] optim with contraints

Adelchi Azzalini azzalini at stat.unipd.it
Sat Jun 21 17:21:59 CEST 2003


There seems to exist peculiar cases where optim does not take care
of constraints on the parameters to be optimized over.  The call to
optim is of the form

  opt <- optim(cp, fn=sn.dev, gr=sn.dev.gh, method="L-BFGS-B",
           lower=c(-Inf, 1e-10, -0.99527), 
           upper=c( Inf, Inf,    0.99527), 
           control=control, X=X, y=y, hessian=FALSE)

The code has worked fine many times, but I have come across cases 
(for suitable data X and y) where the constraint on the last component 
is ignored;  that means that a call is made to sn.dev with
       cp = -1.3546  0.4645  3.1741
so the third component exceeds 0.99527, and the program stops 
because of a check in the  function to be obtimised.

The call just before was to the gradient function
sn.dev.gh: gradient =    219013   -312643 441647332
which has rather large values.

To make the problem more interesting, it shows up on a Linux
(Debian) installation, but it works fine on MS-windows.
In both cases, R is 1.7.0.  

Perhaps this sort of question should not be directed to the R-help
list, rather to the developer(s) of optim. Please instruct me on this 
point. Also, I appreciate that the above is not a reproducible example;
this would be longish in text, and I though to ask first to whom 
it is appropriate that I direct my question.


Best wishes,

Adelchi Azzalini


-- 
Adelchi Azzalini  <azzalini at stat.unipd.it>
Dipart.Scienze Statistiche, Università di Padova, Italia
http://azzalini.stat.unipd.it/




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