[Ifeffit] max number of restraints
Matt Newville
newville at cars.uchicago.edu
Sat Apr 14 14:56:24 CDT 2007
Hi Victor,
> I am confused.
I think Bruce had the same idea as you: Because each restraint is
appended to the vector to be minimized in the least square sense, the
important quantity is
Sum_restraints ( restraint_i)^2
and so you could just do that ahead of time, and then say that
sqrt(Sum_restraints[restraint_i^2]) is a good substitute for the set
of restraints. It does have the appealing feature that it separates
there interdependence compared to a simple addition (where you could
easily get competition between restraints).
I think adding in quadrature is not quite right, as not only is the
minimum of chi-square important, but also the ability to find the
minimum and explore the parameter space. By adding in quadrature, you
prevent the restraints from being negative. Well, the sign *is*
arbitrary (is it data-model or model-data??), but the ability to
switch signs is important.
I am not sure whether adding in quadrature is worse than a simple
addition, but neither is ideal. For sure, having enough individual
restraints is the best approach.
--Matt
More information about the Ifeffit
mailing list