Dear Fraser, The error means that one of internal design matrices in arrayWeights (the one used to model the variances) has gone singular. It is hard to diagnose the problem exactly, but I suggest you try a smaller design matrix for which all the columns are estimable. Although this is a slightly different issue, arrayWeights generally works best when the number of coefficients is much smaller than the number of arrays. You might even use a smaller design matrix for arrayWeights than you use for your lmFit. Best wishes Gordon > Date: Fri, 6 Feb 2009 09:41:47 -0500 > From: "Sim, Fraser" <fraser_sim at="" urmc.rochester.edu=""> > Subject: [BioC] Limma: Array weights question > To: <bioconductor at="" stat.math.ethz.ch=""> > Message-ID: > <82377DC24E19614291D0B5A4A89DAD74DBAB95 at e2k3ms5.urmc- sh.rochester.edu> > Content-Type: text/plain; charset="us-ascii" > > Hi, > > I am trying to use arrayWeights on a design as follows: > >> design = model.matrix(~-1+phenotype+SID) > > Where SID refers to matched samples and phenotype as a cell phenotype > obtained from those samples. > > I run array weights: > >> arrayw <- arrayWeights(eset, design = design, trace = TRUE) > Coefficients not estimable: SIDC4 SIDP5 SIDSG7 > Error in chol.default(Zinfo) : > the leading minor of order 48 is not positive definite > > What does this error mean? > > Here is a summary of the samples. The phenotypes are labeled a through > k. > >> colSums(design) > a b c d e f g h i j > k > 3 4 4 4 4 5 5 5 5 5 > 5 > SID129 SID139 SID92 SIDC1 SIDC2 SIDC3 SIDC4 SIDP1 SIDP2 SIDP3 > SIDP4 > 4 3 4 1 1 1 1 2 2 2 > 2 > SIDP5 SIDSG3 SIDSG4 SIDSG5 SIDSG6 SIDSG7 > 2 4 4 4 4 4 > > > Thanks, > Fraser > >> sessionInfo() > R version 2.8.1 (2008-12-22) > i386-pc-mingw32 > > locale: > LC_COLLATE=English_United States.1252;LC_CTYPE=English_United > States.1252;LC_MONETARY=English_United > States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252 > > attached base packages: > [1] tools stats graphics grDevices utils datasets methods > > [8] base > > other attached packages: > [1] limma_2.16.4 RODBC_1.2-4 hgu133plus2cdf_2.3.0 > [4] affy_1.20.2 Biobase_2.2.1 rcom_2.0-4 > [7] rscproxy_1.0-12 > > loaded via a namespace (and not attached): > [1] affyio_1.10.1 preprocessCore_1.4.0