[BioC] GCRMA/RMA bimodal distribution

[Zhijin Wu]

> 
> Sorry for including the developers, but I guess you are the only ones
> that will be able to answer this, (and I'm not sure BioC accepts .docs).
> I saw a comment from Jean addressing the same question but couldn't find
> the reply he referred to. 

The original questioin I got was about the bimodal distribution of gcrma
result from probe intensities with unimodel distribution. My answer was
that the "change" was not necessarily surprising.

For example , when you have "true log signal" from a bimodal distribution
logS=c(rnorm(1000,3,1),rnorm(1000,8,2))
# You will see this has two peaks
par(mfrow=c(2,2))
plot(density(logS))
#if the background, log(non-specific binding) come from 
logB=rnorm(2000,6,1)
#then when you plot the histogram of convolution in log scale,
plot(density(log(exp(logS)+exp(logB)))) 
#you see only one peak, and this would be "before gcrma".