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Re: newbie question about the symbol E

• To: mathgroup at smc.vnet.net
• Subject: [mg28318] Re: newbie question about the symbol E
• From: "Paul Lutus" <nospam at nosite.com>
• Date: Wed, 11 Apr 2001 02:00:57 -0400 (EDT)
• References: <9arn5o$qna@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

"Martin P. Pos" <posmpxxxx at xxxxhome.nl> wrote in message
news:9arn5o$qna at smc.vnet.net...
> I want to declare a function of energy E, say f[E], but mathematica
doesn't
> allow me to use E as a symbol, because it is reserved for the exponential
> constant. In the frontend I use <esc>ee<esc> to enter that exponential
> constant, but i want E to be the variable of this function.
>
> Similar, I can declare a constant, e.g.:
>
> Subscript[E, F] := 10
>
> But when I do:
>
> Clear[Subscript[E, F]]
>
> mathematica responds:
>
> "Clear::ssym : eF is not a symbol or string"
>
> where eF is the exponential constant, subscript F.
>
> I want to enter the following formula:
>
> f[x_] := 1/(1 + E^((Subscript[x, F] - x)/(k*T)))
>
> where E should be the exponential constant and x should be E (capital e)
>
> Is there a way to do what I want, or is it not possible to use E?

In your last example, you are asking to use "E" for two different purposes
in the same equation. You cannot do this. Use a different letter. Then, when
the computation is finished, put the result in a string and replace whatever
letter you choose with E.

Example:

f[x_] = 1/(1+E^(f - x)/(k T))

a = StringReplace[ToString[f[x]],"E"->"e"]

b = StringReplace[a,"x"->"E"]

Something like that.

--
Paul Lutus
www.arachnoid.com