etime: Elapsed Time Since Start of Execution (Fortran Library Reference)

Fortran Library Reference

`etime`: Elapsed Time Since Start of Execution

For etime, the elapsed time is:

Single Processor-CPU time for the calling process
Multiple Processors--wallclock time while processing your program

Here is how FORTRAN decides single processor or multiple processor:

For a parallelized FORTRAN program linked with libF77_mt, if the environment variable PARALLEL is:

Undefined, the current run is single processor.
Defined and in the range 1, 2, 3, ..., the current run is multiple processor.
Defined, but some value other than 1, 2, 3, ..., the results are unpredictable.

The function is called by:

`e= etime(tarray` `)`
`tarray`	`real(2)`	Output	`e`= -1.0: Error: `tarray` values are undefined. `e`¬= -1.0: Single Processor: User time in `tarray(1)`. System time in `tarray(2)` Multiple Processor: Wall clock time in `tarray(1),` 0.0 in `tarray(2)`
Return value	`real`	Output	`e`= -1.0: Error `e`¬= -1.0: The sum of `tarray(1)` and `tarray(2)`

e= etime(tarray )

tarray

real(2)

Output

e= -1.0: Error: tarray values are undefined.

e¬= -1.0: Single Processor: User time in tarray(1). System time in tarray(2)

Multiple Processor: Wall clock time in tarray(1), 0.0 in tarray(2)

Return value

real

Output

e= -1.0: Error

e¬= -1.0: The sum of tarray(1) and tarray(2)

Take note that the initial call to etime will be inaccurate. It merely enables the system clock. Do not use the value returned by the initial call to etime.

Example: etime(), single processor:

    real e, etime, t(2)
    e = etime(t)         !  Startup etime - do not use result
    do i = 1, 10000
        k=k+1
    end do
    e = etime( t )
    print *, 'elapsed:', e, ', user:', t(1), `, sys:', t(2)
    end
demo% f77 -silent tetime.f
demo% a.out
elapsed:   0.190000, user:    6.00000E-02, sys:   0.130000
demo%

See also times(2), f77(1), and the Fortran Programming Guide.