[chemfp] infinite similarity measures

[Andrew Dalke]

What value should Tanimoto(fp1, fp2) return when fp1 and fp2 have no bits set?

In that case: c / (a+b+c) = 0/(0+0+0) = 0/0 .

I've defined it in my code as 0.

I could return an IEEE infinity value, which is what OpenBabel and CDK do.

I could also define them as 1.0, which is what OpenEye does.


The same question applies if I were to implement some of the other measure from

  http://www.daylight.com/dayhtml/doc/theory/theory.finger.html

What in general should be returned when the result is infinity?


				Andrew
				dalke at dalkescientific.com
P.S.
 I think the answer to this is also why a raven is like a writing desk. :)