channel 2 signal !G 93 # 93 slides background !G 93 dart.asd !ASUV signal ~ Trait.channel Trait.channel.vect(back) ...to fit a slide specific regression of signal on background. In this example, signal is a multivariate set of 93 variates and back is a set of 93 covariates. The vect() function strings out the covariate values in the same manner that the response variables are processed. The signal values relate to either the Red or Green channels. So for each slide and channel, we need to fit a simple regression of signal ~ mu back. But the data for the 93 slides is presented in parallel. If it were presented in series, with a factor slide indexing the slides, the equivalent model would be signal ~ slide.channel slide.channel.back.