[phenixbb] Planarity restraint ignored when dist_esd equal to 0

[Pavel Afonine]

Hi Keitaro,

> Yes, it would be problematic if 0 is not treated specially. What we
> normally expect might be the planarity constraint if sigma is 0.

with this logic you interpret the number and not use it. Follow this 
road you may end up with odd things, like let's treat 0 as 
"constraints", 0.1 as "strong restraints", 1.5 as "weak restraints", etc 
and in each case do something very different - I hope you get the idea.

What's done currently is there is a number, there is a formula that this 
number goes into, and there is a piece of code that uses the number and 
formula in a way to avoid numeric issues. As simple as this, no 
connotations involved.

I believe using 0 as a trigger to tell that you want something else than 
what these numbers are used for otherwise is not the best way (why not 
put None or something?).

All the best,
Pavel