Dear Correlator,

did the defaults to 3ddot change recently?

I just tried 3ddot with and without the -demean option and it gives identical results...

By the way, I see now... perhaps...a reason for wanting *not* to demean: if trying to assess the similarity between two maps whose intensity values are meaningful in their sheer magnitude, not only in their relative spatial distribution (e.g., when comparing two Z-maps), then it may be better not to demean (if we demean, two Z-maps with similar spatial structure but very different z-magnitudes will be assigned a high similarity coefficient by the output of 3ddot). May I dare to believe to have caught a glimpse of the Correlator's infinite foresight for this usage of 3ddot without demean?

With regard to this, when 3ddot is run without the -demean option is it the following formula

sum(x)sum(y)/sqrt(sum(x^2)*sum(x^2))

which actually gets computed?
( I tried to read the code, but didn't succeed much....)


devoutly,

g.