I use the function timef (module IFLPORT) to measure the elapsed time of my executable. I called it at the beginning and again at the end of the computations. In most cases the elapsed time is correct. However, sometimes I get a negativ elapsed time.
Any ideas what went wrong?
The kind of behavior described in #1 happens if, as Andrew surmised, the value returned by the nonstandard extension TIMEF() is assigned to a single-precision real, AND the compiler is not told that TIMEF is of type DOUBLE PRECISION.
Either add USE IFPORT to your program unit that calls TIMEF(), or declare TIMEF as DOUBLE PRECISION in that unit.