[BioC] negative values in from pmonly in dChip

[Wenqiong Chen]

Hi, everybody:
Can someone point to me that if it is possible to get negative values from
the following command?
expresso(data, normalize.method="invariantset", bg.correct=F,
pmcorrect.method="pmonly", summary.method="liwong")

I thought that if I used "pmonly" there should be no negative values,
especially when no background correction was applied. Did I miss anything? I
am sure I did.
Thanks a lot for your help!
wenqiong