Thanks, The problem is solved, I was writing 'aa=ave(s,t=it1,t=it5)'wheras it should have been 'aa=ave(swh,t='it1',t='it5')'Raj -------------- next part -------------- An HTML attachment was scrubbed... URL: http://gradsusr.org/pipermail/gradsusr/attachments/20090226/bdb5a947/attachment.html