Hi, It looks like when VecWAXPY is called with alpha=Nan, PetscValidLogicalCollectiveScalar causes the message "Scalar value must be same on all processes, argument # 2" to be printed. This is a bit misleading, and confusing when running on only 1 processor. Is this something worth fixing? Blaise -- Department of Mathematics and Center for Computation & Technology Louisiana State University, Baton Rouge, LA 70803, USA Tel. +1 (225) 578 1612, Fax +1 (225) 578 4276 http://www.math.lsu.edu/~bourdin