Javier Ángel Velázquez Muriel wrote:
> I am going to suggest something that is not very "correct", but that it
> is already "de facto" in IMP. I would suggest a default epsilon value
> for the cases where the use of "almost_equal" function cannot be
> avoided. That is dangerous, I know, but I think it is even more
> dangerous to have the code full of different epsilons if they don't need
> to be different.
>
> I'm saying this because IMP::em already has a EPS value of 1e-6 that is
> thoroughly used, and probably makes sense to define one EPS in other
> modules.
I disagree. You can't have "one true epsilon" because it depends on what
you are comparing. If you are comparing two numbers which are themselves
around 1e-6, that epsilon value is useless, for example. And in many
cases, it makes sense to use a percentage.
> My need is to compute the correlation between two em::Images, that in
> fact is going to be the correlation between their algebra::MultiArrays
> containing the data, and I need to check for values of the standard
> deviation (which is a double) near zero. I don't see how to avoid the
> use of almost_equal() here, and again, a default epsilon for
> IMP::algebra sounds reasonable to me.
Well, of course you will need an "almost_equal" function, because you
can't compare two floating point numbers exactly in most circumstances.
But a "default epsilon" makes no sense.
Ben
--
http://salilab.org/~ben/
"It is a capital mistake to theorize before one has data."
- Sir Arthur Conan Doyle