Jed: I have been awake since 1 AM so my mental fidelity is low. I use format specifiers in a consistent way across I/O functions. For e.g. scanf, you need to do as I indicated, although you are correct that printf does not care. Tania: Try clock_gettime(MONOTONIC) instead. Jeff On 2/21/17, 5:22 AM, "Jed Brown" <[email protected]> wrote: "Hammond, Jeff R" <[email protected]> writes:

MPI wtime returns a double. You are printing as a float so half the bits are lost. Try %lf.

WUT? %f is for doubles. It actually isn't possible to pass float through varargs, they are implicitly promoted. Tania, have you printed t2-t1? The absolute value is of no significance.