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MathGroup Archive 2005

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Re: Re: Get numbers out of PhysicalConstants?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg62638] Re: [mg62595] Re: Get numbers out of PhysicalConstants?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Wed, 30 Nov 2005 00:06:19 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Chris,

I think it should be exact and I even once modified the package code, but
didn't carry it along from version to version.

Using my ExtendUnits package it is quite easy to get rid of the units.

Needs["Units`ExtendUnits`"]
Needs["Miscellaneous`PhysicalConstants`"]

For SI units...

VacuumPermittivity
% // Deunitize
(8.854187817*^-12*Ampere*Second)/(Meter*Volt)
8.854187817*^-12

For CGS units...

VacuumPermittivity // Deunitize[#, {}, CGS] &
8.854187817*^-14

And if one has an function that involves units with input variables and
parameters and an output value with units, then the DeunitizeWithReference
routine can be used to deunitized with any compatible implied input units
and any desired implied output unit.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/


From: Chris Chiasson [mailto:chris.chiasson at gmail.com]
To: mathgroup at smc.vnet.net


Replace the units with 1s?

ReplaceAll[VacuumPermeability,Rule[Alternatives[Second,Volt,Ampere,Meter],1]
]

or

VacuumPermeability/.\[InvisibleSpace]Second|Volt|Ampere|Meter\[Rule]1

By the way, given the definition of VacuumPermittivity, do you think
the magnitude of VacuumPermittivity should be exact like
(1/(VacuumPermeability*SpeedOfLight^2)) or that it should be the
MachinePrecision value it current is?

Full disclosure: I think it should be exact, even though others on the
list seem to disagree.

Regards,
--
http://chrischiasson.com/contact/chris_chiasson



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