The attached file "equation" in my previous e-mail does not go through (It was created by Microsoft word). I re-type the equations in Notepad and attach it now. Mei-Chu Lo -------------- next part -------------- An embedded and charset-unspecified text was scrubbed... Name: equation.txt Url: https://stat.ethz.ch/pipermail/r-help/attachments/20030609/d959f116/equation.txt