Re: Get numbers out of PhysicalConstants?
- To: mathgroup at smc.vnet.net
- Subject: [mg62616] Re: Get numbers out of PhysicalConstants?
- From: dh <dh at metrohm.ch>
- Date: Tue, 29 Nov 2005 06:43:19 -0500 (EST)
- References: <dme8l6$inj$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi Wonseok,
One way to achieve what you want is to replace all the units by 1.
Toward this aim you may use a function from Miscellaneous`Units`Private`
called UniqueCasesUnit:
UniqueCasesUnit[expr_]:=
Union[Cases[
expr,_Symbol?((MatchQ[#,_Symbol]&&(MemberQ[{"Miscellaneous`Units`",
"Miscellaneous`SIUnits`"},Context[#]]||
MemberQ[{Second,Newton,Degree,Circle,Point,Last,Drop,
Gamma,Byte},#]))&),Infinity]]
that gives you the units of an expression.
With this we can extract the numerical part of an expression by e.g.
VacuumPermeability:
<< Miscellaneous`PhysicalConstants`
<< Miscellaneous`Units`
(t = VacuumPermeability) /. ((# -> 1) & /@ \
Miscellaneous`Units`Private`UniqueCasesUnit[t])
Daniel
Wonseok Shin wrote:
> Hello,
>
> Is there any way to get numbers out of the constants defined in
> Miscellaneous`PhysicalConstants` package? Carrying units all the time
> is inconvenient in calculation.
>
> For example,
> In[1]:= << Miscellaneous`PhysicalConstants`
> In[2]:= VacuumPermeability
> Out[2]= \!\(\(p\ Second\ Volt\)\/\(2500000\ Ampere\ Meter\)\)
>
> I want to get the number p/2500000 out of VacuumPermeability, without
> units. How can I do this?
>