about "_solve_time"

[andr...@yahoo.com]

Hi,

I'm using AMPL to code some algorithms and want to compare the solving
time. I know AMPL's internal variable "_solve_time" is the sum of
various system and user time. Could someone explain to me what the
differences and relationships are among those time, at least to the
following four time?

_ampl_elapsed_time
_ampl_system_time
_total_solve_elapsed_time
_total_solve_system_time

Also, what's the difference between user time and system time?

Thanks,
Andrew

[Robert Fourer]

Copied below are all the built-in timing parameters, from page 496 of the AMPL
book (2nd edition). In general, the "elapsed" time of a process is the time
that you would measure using a stopwatch or other clock not connected to the
computer, from the time when the process began to run until the time that it
finishes. The "system" and "user" times are the computer's estimates of how
much processor time the process took; this is generally a smaller number than
elapsed time, because there are many processes sharing the processor's time.
The distinction between system and user time is defined by the operating
system, but for most purposes it suffices to keep track of their sum.

The "ampl" times refer to the AMPL system's process, while the "total_solve"
times refer to the summed times of all the solver calls. Thus
_ampl_elapsed_time includes the _total_solve_elapsed_time, while the _ampl_time
does not include the _total_solve_time.

Bob Fourer
4...@ampl.com

_ampl_elapsed_time elapsed seconds since the start of the AMPL process
_ampl_system_time system CPU seconds used by the AMPL process itself
_ampl_user_time user CPU seconds used by the AMPL process itself
_ampl_time _ampl_system_time + _ampl_user_time
_shell_elapsed_time elapsed seconds for most recent shell command
_shell_system_time system CPU seconds used by most recent shell command
_shell_user_time user CPU seconds used by most recent shell command
_shell_time _shell_system_time + _shell_user_time
_solve_elapsed_time elapsed seconds for most recent solve command
_solve_system_time system CPU seconds used by most recent solve command
_solve_user_time user CPU seconds used by most recent solve command
_solve_time _solve_system_time + _solve_user_time
_total_shell_elapsed_time elapsed seconds used by all shell commands
_total_shell_system_time system CPU seconds used by all shell commands
_total_shell_user_time user CPU seconds used by all shell commands
_total_shell_time _total_shell_system_time + _total_shell_user_time
_total_solve_elapsed_time elapsed seconds used by all solve commands
_total_solve_system_time system CPU seconds used by all solve commands
_total_solve_user_time user CPU seconds used by all solve commands
_total_solve_time _total_solve_system_time + _total_solve_user_time