.\" @(#)etime.3f 1.6 86/01/02 SMI; from UCB 4.2
.TH ETIME 3F "98/09/16"
.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.
.LP
Time is in number of seconds.
The resolution is to a nanosecond.
.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"