strange initial value behavior about iminuit HOT 8 CLOSED

I have a guess why that is. There is an internal and external variable inside minuit. Some function takes internal and some take external... I think I have screwed it up somewhere.

from iminuit.

Upon investigation, Minuit does not really support one-sided limit. When a parameter is constructed, it's either unbounded or bounded. The minimization algorithm only works for unbounded one. So the trick is to transform unbounded one bounded one is transformed to unbounded one with arctan or something similar which needs the bound both sides.

The current behavior is just plain wrong since the parameter is constructed as unbounded and bound is put in later so there will be no transformation there.

Some note on one-sided there.

One sided limits: It is common that one needs to restrict a particular parameter only on one side---for example, to be non-negative. If the user decides to set limits, in this case there is a temptation to set the upper limit to some very large number. This is sure to cause major problems (see the manual). It would be better to set the limits so that the location of the minimum is roughly midway between the lower and upper limit. But limits should only be used when they are really needed---if Minuit does not drift into the parameter's illegal region, no limit is needed for that parameter.

see more:http://www-cdf.fnal.gov/physics/statistics/recommendations/minuit.html

from iminuit.

I'll revert back to the old behavior then. Sorry no one sided limit. :(

from iminuit.

Oh well. Sorry for suggesting one sided limits, thought it would be trivial!

from iminuit.

I thought that too. But this really need to be fixed.

from iminuit.

Limits and one sided limit should be working properly in 1.1.0

from iminuit.

Can this issue be closed?

With the current iminuit version I get this: http://nbviewer.ipython.org/gist/cdeil/45b0e71159abcdf2541f

@piti118 Would it be useful to add this example as a test case or is this already covered by other tests?

from iminuit.

Closing this issue ... let me know if there's something left to do and we can re-open (or file a new one).

from iminuit.