It seems that BLAS sdot_ in OX X Lion actually returns "double" instead of "float". I'm using the attached patch with success. Of course, it would need a proper configure test that I'm not in position to provide but Matt volunteered to write. Can any of you (Sean?) running Lion try to reproduce the issue using configure --with-precision=single && make all && make test , and then try my patch? -- Lisandro Dalcin --------------- CIMEC (INTEC/CONICET-UNL) Predio CONICET-Santa Fe Colectora RN 168 Km 472, Paraje El Pozo 3000 Santa Fe, Argentina Tel: +54-342-4511594 (ext 1011) Tel/Fax: +54-342-4511169