[Ifeffit] Hard restraints?

[Bruce Ravel]

Hi folks,

I am sitting here at the beamline waiting for data to roll in and reading the 
mailing list correspondence that came in while I was on vacation.  A month 
ago Scott and Matt had a very interesting discussion about ways to set 
boundaries on parameter values in fits.  Matt showed a rather complicated 
math expression using Ifeffit's current restraint mechanism that does 
essentially the same thing as the hypothetical expression 
"bound(x,lo_val,hi_val)", where "x" is a guessed parameter, and the other two 
numbers indicate the boundaries beyond which a severe penalty should be 
applied to the fitting metric.  Matt's expression was, as Scott, said rather 
fiendish and clever.  Norbert then piped up suggesting that a "bound" would 
be widely appreciated.

One solution is, of course, to wait for Matt to find the time to implement and 
test a bound function.  It occurs to me that another solution is to implement 
in Artemis a "bound" interface which would take the arguments of the 
hypothetical bound function mentioned in the last paragraph and construct the 
long expression that Matt suggested to Scott.  All that could be done (as so 
many things are) behind the scenes and out of view of the casual user.

The Artemis solution has two nice features.  One is that it would be much more 
transparent to the user than trying to implement Matt's fiendish suggestion 
by hand.  The second is that I could probably deliver this feature pretty 
quickly in Artemis and it may not be necessary to change Ifeffit.

Scott and Norbert seem interested, so perhaps I should put this on the list of 
things to do...

B