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<p><font face="serif">I know that some of you are starting to work
on the diffusion problem. Let me alert you to something that
you have to be VERY cautious about. In your physical simulation
you have to conserve mass. If you look at the java code I gave
you, I keep up with a variable called "sumval" which is the
total number of the particles across the entire cube. It starts
out at 1x10^21 and should remain basically at that value during
the entire simulation. You will notice some slight variation
when you run the Java code, but pay close attention to where the
number is actually changing -- it is changing at the very edge
of the last digit of precision. The point is that the
simulation, as it runs, does not gain or lose mass -- mass is
conserved.</font></p>
<p><font face="serif">As you implement this code in other languages
make sure that mass is conserved. <br>
</font></p>
<p><font face="serif">Many of you will want to try and speed it up
(I mean do you really need all those nested loops) - but if you
do the actual simulation time should be roughly the same and the
mass must be conserved.</font></p>
<p><font face="serif"><br>
</font></p>
<div class="moz-signature">-- <br>
<b><i>Andrew J. Pounds, Ph.D.</i></b><br>
<i>Professor of Chemistry and Computer Science</i><br>
<i>Director of the Computational Science Program</i><br>
<i>Mercer University, Macon, GA 31207 (478) 301-5627</i></div>
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