Physical constants and their evaluation
- To: mathgroup at smc.vnet.net
- Subject: [mg18107] Physical constants and their evaluation
- From: John JOWETT <John.Jowett at cern.ch>
- Date: Thu, 17 Jun 1999 12:26:41 -0400
- Delivery-date: Thu Jun 17 16:21:22 1999
- Organization: CERN
- Sender: owner-wri-mathgroup at wolfram.com
Hello,
I am wondering about the best policy for evaluating physical
formulas containing fundamental constants and the like. I have often
used rules as in
Needs["Miscellaneous`PhysicalConstants`"]
evaluateConstants={me->ElectronMass,
hbar->PlanckConstantReduced,
c->SpeedOfLight}
that can be applied when desired to a symbolic expression such as
(1.234 me hbar/c) /. evaluateConstants
to get numerical values with units. Up until then, the expressions
contain the constants symbolically
Another approach would be to define
N[me] = ElectronMass;
N[hbar] = PlanckConstantReduced;
N[c] = SpeedOfLight;
and then just use N[...] when the time comes to "plug in numbers".
Is there any reason to prefer one method over the other? I'd like to do
the right thing as I plan to build up fairly elaborate packages on this
basis.
Thanks for any suggestions,
John Jowett
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