Fortran Wall Clock Time

Time in seconds since an arbitrary time in the past.

Fortran wall clock time. When timing a fortran program i usually just use the command call cpu time t. The date and time subroutine returns data from the real time clock and the date. System clock cpu time date and time these all appear to use various of the system routines. I was not trying to say that cpu time and system clock are the same but that both these fortran standard routines use timing sources that are updated every 1 64th of a second.

If no time source is available time is set to 1 0. The fortran intrinsics are. Getprocesstimes suffers from poor resolution when i have tested it. Intel fortran compiler 19 1 developer guide and reference.

For details see fortran library reference manual or the individual man pages for these functions. For cpu time the absolute value is meaningless only differences between subsequent calls to this subroutine as shown in the example below should be used. See mpi wtick to determine the resolution of mpi wtime. My knowledge of these come from.

Developer guide and reference. This is a fortran 77 version of the fortran 90 intrinsic routine and is year 2000 safe. The routines listed in the following table provide compatibility with vms fortran system routines idate and time to use these routines you must include the lv77 option on the f77 command line in which case you also get these vms versions instead of the standard f77 versions. If the attribute mpi wtime is global is defined and true then the value is synchronized across all processes in mpi comm world.

Local time is returned as well as the difference between local time and universal coordinated time utc also known as greenwich mean time gmt. 07 15 2020 public content download as pdf. Fortran 95 and later class. For use as a timing routine with the speed of modern processors this is a very poor precision to provide.

Again my experience is limited to the win environment. Get date and time. 9 265 system clock time function description. It is most often used for measuring or tracking the time spent in code blocks in lieu of using profiling tools.

Then i stumbled across call system clock count count rate count max which seems to do the same thing. However in a more difficult manor. Getprocesstimes is the only routine to return cpu time while the others return elapsed time. Determines the count of a processor clock since an unspecified time in the past modulo count max count rate determines the number of clock ticks per second.

Notes this is intended to be a high resolution elapsed or wall clock. If the platform supports a monotonic clock that clock is used and can depending on the platform clock implementation provide up to nanosecond resolution. Note that time may contain a system dependent arbitrary offset and may not start with 0 0.