.\" @(#)etime.3f 1.6 86/01/02 SMI; from UCB 4.2
.TH ETIME 3F "00/01/25"
.SH NAME
etime, dtime \- return elapsed time
.SH SYNOPSIS
.B real function etime (time)
.br
.B real time(2)
.sp 1
.B real function dtime (time)
.br
.B real time(2)
.\"
.SH DESCRIPTION
These functions return elapsed time in seconds.
.LP
The versions of 
.B etime
and 
.B dtime
used by 
.B f77
return times produced by the runtime system's high
resolution clock. The actual resolution depends on
the system platform.  The resolutions of the clocks on current
platforms range between one nanosecond and one microsecond.
.LP
Versions of 
.B etime
and
.B dtime
used by 
.B f95
use the system's low resolution clock by default, the
resolution of which is one hundreth of a second. However, if
the program is run under the SunOS utility 
.BR ptime ,
( /usr/proc/bin/ptime), 
.B etime
and
.B dtime
use the high resolution clock.

.LP
.I NOTE:
The very first call to 
.B etime
or
.B dtime
may be inaccurate. 
.LP
If there is an error:
.IP \(bu 2
Argument elements
.B time(1)
and
.B time(2)
are
.I undefined
.IP \(bu 2
Function return value = -1.0
.LP
If there is no error:
.IP \(bu 2
Argument:
.I "user time" 
in 
.B time(1)
and 
.I "system time"
in
.B time(2)
.IP \(bu 2
Function return value: sum of
.B time(1)
and
.B time(2)
.LP
.B dtime
returns the elapsed time since the last call to
.BR dtime .
.LP
For
.BR dtime ,
the elapsed time is:
.IP \(bu 2
On the first call,
elapsed time since the start of execution
.IP \(bu 2
On the second and subsequent calls,
the elapsed time since the last call to
.B dtime
.IP \(bu 2
For 
.IR "single processor" , 
the time used by the CPU
.IP \(bu 2
For 
.IR "multiple processors" ,
the sum of times for all the CPUs
(not useful, use 
.BR etime )
.br
.IR Note :
Do not call
.B dtime
from within a parallelized loop.
.LP
.B etime
returns the elapsed time since the start of execution.
.LP
For
.BR etime ,
the elapsed time is:
.IP \(bu 2
For 
.IR "single processor" :
the CPU time for the calling process
.IP \(bu 2
For 
.IR "multiple processors" :
the wall-clock time while running your program
.br
.IR Note : 
.B time(1)
contains the wall clock time;
.B time(2)
is 0.0.
.LP
.B f77 
determines single versus multiple processing 
depending on whether a program is linked with the multithreaded
version of the FORTRAN 77 library,
.BR libF77_mt ,
and if the environment variable 
.B PARALLEL
is:
.TP
Undefined,
then the current run is
.IR "single processor" .
.TP
Defined, and in the range 1, 2, 3, ...,
then the current run is
.IR "multiple processor" .
.TP
Defined, but some value other than 1, 2, 3, ...,
then the results are unpredictable.
.\"
.SH FILES
.\"
.BR libF77.a ,
.BR libF77_mt.a ,
.BR libF77.so ,
.BR libF77_mt.so
.\"
.SH "SEE ALSO"
.\"
.BR times (2),
.BR f77 (1),
.I "Fortran User's Guide"
and the 
.I "Fortran Library Reference"