Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!ucsd!ucbvax!bloom-beacon!oliver
From: oliver@athena.mit.edu (James D. Oliver III)
Newsgroups: comp.lang.fortran
Subject: Re: Random Number Functions--Generate versus Input
Message-ID: <1990Nov8.215752.7075@athena.mit.edu>
Date: 8 Nov 90 21:57:52 GMT
References: <1990Nov8.170334.24579@athena.mit.edu>
Sender: daemon@athena.mit.edu (Mr Background)
Organization: Massachusetts Institute of Technology
Lines: 21

I guess I need to make this clear: the random number genertor itself is
vectorizable, however, the values of interest to me are *functions* of
these randome variables.  To be more specific, I'm generating a series of
randomly oriented 3-D unit vectors.  The fastest way to do this is to
generate two random numbers for x and y and calculate z as long as x**2 +
y**2 <= 1.  This process, however, involves a conditional loop back to the
ranf() function and thus is not vectorizable.  However, the fact that this
method is not vectorizable is just of incidental interest, since it remains
the fastest way of doing it.

What I'd like to know is, *given* this way of generating my values, should
I expect it to be faster than reading the values from a file?  Like I said,
for this particular case I can run a benchmark, but I was wondering if
there was a general rule of thumb for the speed of I/O operations.


--
____________________________
	Jim Oliver   
	oliver@athena.mit.edu /	joliver@hstbme.mit.edu
	oliver%mitwccf.BITNET@MITVMA.MIT.EDU