Hello Michael, On Sun, 2011-04-24 at 02:54 +0000, Michael D. Berger wrote: > cerr << "some stuff" << endl; > mat3 = matmult(mat1,mat2); > > I get a difference of the order 1.0e-15 depending on whether the > cerr line does or does not end in "endl" as shown. If the exact same input produces different results depending on whether or not you add and endl before the function call would probably count as a bug. Could be something like a status bit that does not get cleared when it should be. However, since this is such a gcc specific issue I would suggest you take this upstream: http://gcc.gnu.org/lists.html . People there will probably be able to help you better than the people on this list. Regards, Leonard. -- mount -t life -o ro /dev/dna /genetic/research