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Given an nxm matrix A I want to compute the nxm matrix B whose ij-th element is the sum of the elements of A lying on the diagonal that ends with element ij, i.e., b_ij = a_ij + a_(i-1)(j-1) + a_(i-2)(j-2) + ... In APL (which I no longer use), I would use the 'rotate' operator to derive an array whose columns are diagonals of the given array and then cumulate down columns. Is there a similar operator in R, or is there another/better way? -.-.-.-.-.-.-....

All, How does one specify a model in lmer such that say the random effect for the intercept has a different variance per treatment group? Thus, in the model equation, we'd have say b_ij represent the random effect for patient j in treatment group i, with variance depending on i, i.e, var(b_ij) = tau_i. Didn't see this in the docs or Pinherio & Bates (section 5.2 is specific for modelling within group errors). Sample repeated measures code below is for a single random...

Hi al, I have a dataset (see attached), which basically involves 4 treatments for a chemotherapy drug. Samples were taken from 2 biopsy locations, and biopsy were taken at 2 time points. So each subject has 4 data points (from 2 biopsy locations and 2 time points). The objective is to study treatment difference.? I used lme to fit a mixed model that uses "biopsy.site nested within pid"