🚀 go-pugleaf

Since this is a computer-related question, I can understand if this
question would be better asked elsewhere, so pointers to where it belongs
are welcomed.

We have an application where we are trying to estimate the order of
a certain algorithm (whether O(N), O(N^2), etc.) by running it a certain
number of times for various values of N.  We measure the CPU time used
by the algorithm using the FORTRAN "SECNDS" command, executing it just 
before and just after the algorithm runs through its paces.

What we are finding is that the CPU measure we get back varies wildly,
even for large values of N (~250) and for large numbers of runs (~30).
The questions are as follows:

(1) Are there aspects of the SECNDS command we don't know about, such as

	o  sensitivity to system functions (user load, time of day, etc.)
	o  inherent uncertainty

(2) Is there a more reliable way to estimate the order of the algorithm?

As you have guessed, we're running in FORTRAN, we're on a shared system,
and we're not taking advantage of parallel processing or any other advanced
programming tool.

Conscientious replies welcomed, will summarize if there is interest.

RG

Who became an engineer thinking "free-body diagrams" might be interesting.