Closed notEvil closed 5 years ago
Seems to be a numerical issue. Such boundary cases are tricky. Any recommendations?
I would add an argument to BiCopTau2Par
which allows Kendall's tau to be moved to closest valid value, for instance mode=c('exact', 'approximate')
, and let BiCopEst
always use 'approxmiate'
. Even if Kendall's tau is completely off (say -0.7 for Clayton), the estimate is still the best among all valid estimates.
I don't really like to add an option for this (there are zero users for 'exact'
). I'd make the function behave like your 'approximate'
.
It will take me a while until I get to all the issues here, I am happy to accept pull requests though ;)
I'll give it a try :)
Check out https://github.com/notEvil/VineCopula/commit/89b614cb6673d5f2f58bb68b3f8448ce7f616430 Its not ready for pull yet because there are a couple of open points:
check.taus
of BiCopTau2Par
obsoleteadjustTau
has a similar goal as BiCopCheck.R/adjustPars
(centralize?)BiCopTau2Par
(callers, tests)(While I checked the code I saw that BiCopEst
and BiCopEst.intern
are almost identical. Probably worth refactoring.)
I don't think check.taus
is obsolete. Kendall's tau should only be adjusted within BiCopEst(.intern)
. If someone calls BiCopTau2Par(4, -0.5)
or BiCop(4, tau = -0.5)
there should still be an error.
Yes, checking is still necessary. Further, I the changes have to be backward compatible. I would change as little as possible. Just enough that it does not break functions in the boundary cases. Thus an approximation at the boundary cases seems to be a possible solution. @notEvil thanks for the suggestions
Sry I misunderstood. I've reverted the changes, added adjustTaus
to file BiCopCheck.R
where adjustPars
already resides and added calls to adjustTaus
in BiCopEst
and BiCopEst.intern
; see https://github.com/notEvil/VineCopula/commit/94008969911e3ce9eda6590047eecc2a96ce7266 (check diff against origin/master)
Hope thats more in line with what you were thinking about.
That looks good, many thanks for your effort! You can open a PR and I'll merge as soon as the checks pass.
Hi,
https://github.com/tnagler/VineCopula/blob/20aea996717ebb797860e9c8ee57c1ab355e69d0/R/BiCopEst.R#L176 fails explicitly if empirical tau is outside of valid range (e.g. tau = -epsilon for Clayton). At least for MLE, parameters should be moved to closest boundary (e.g. 1e-4 for tau = -epsilon for Clayton) in those cases imo.
KR, Andreas