Craig,

I have to disagree with some of your definitions as I use the terms -- I do not 
know how they are defined in the standard, except that they are allowed not to 
be defined :-)

>    The best standard procedure for this purpose is the Fortran **95** 
>subroutine
>CPU_TIME.  It takes a single real argument, which is the elapsed processor time 
>in
>seconds.  The exact definition of the processor time is left imprecise.  If you
>want to time a procedure, you need to call CPU_TIME twice, with two separate 
>actual
>arguments.

(My mail has re-formatted, I've just added a chevron to each line.)

The terms "elapsed" and "processor" time to me are different.  Elapsed is 
wall-clock, and includes all the overheads that a user experiences.  Processor 
time is (if returned by the OS) a measure of the CPU and is what I use for 
comparing timing of algorithms.  The former is irrelevant for determining CPU 
intensive algorithms;  it is also biased by how many users are active on the 
system.

>    Other alternatives include the F90 SYSTEM_CLOCK subroutine and the
>DATE_AND_TIME subroutine.  If you want to time sections of code, you will again
>need to call either of these subroutines twice, with separate sets of arguments 
>for
>the beginning and the end.

These all give (what I term) elapsed time.  Not a true analysis of the merits of 
different algorithms  -- unless on a single user system with no other processes 
running.

>    There is no standard way in F9x to start a timer at one point and then read
>that timer later on.  You will need to create your own timer using one of the
>subroutines I mentioned above.

I dunno :-) :-)

:-) Assuming CPU_TIME returns meaningful results (else use elapsed time), I 
would have thought the following code is standard -- but not a one-liner:

CALL CPU_TIME(T1)
CALL ROUTINE_TO_MEASURE
CALL CPU_TIME(T2)
WRITE(*,*) 'Time taken ' , T2-T1
:-)

Hmmm, I'm not a UNIX person ( -- VMS), does the time command measure CPU time or 
wall-clock time?  If the latter, it is **not** a good measurement of relative 
algorithms on a multi-user system.  Using elapsed time, I can see situations 
where bubblesort could beat quicksort.  {On a multi-user system heavily loaded, 
a batch process running quicksort on a low priority could take longer wall-clock 
than an interactive bubblesort on a higher prority -- I frequently see similar 
situations on my production machine.]


>varadharajan wrote:
>
>> Hello!
>> I wanted to  know if there is some F90 command to time subroutines and
>> functions withing programs. Whole programs can be timed by the time
>> command in unix but what about subroutines within? Is there such a
>> facility?
>>
>> Regards,
>> Varadharajan S

Regards, Paddy

Paddy O'Brien,
Transmission Development,
TransGrid,
PO Box A1000, Sydney South, 
NSW 2000, Australia

Tel:   +61 2 9284-3063
Fax:   +61 2 9284-3050
Email: [log in to unmask]

Either "\'" or "\s" (to escape the apostrophe) seems to work for most people,
but that little whizz-bang apostrophe gives me little spam.



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