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Re: question

• To: mathgroup at smc.vnet.net
• Subject: [mg7113] Re: [mg7085] question
• From: seanross at worldnet.att.net
• Date: Sun, 11 May 1997 02:57:13 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

Dr. Tar Ortiz wrote:
> 
> We want to plot the function x=4 , but we can not do that. Do you know
> how to do it, help us please.
> --
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> Dr. Tar Ortiz Peralta                        Instituto Tecnológico y de
> Estudios Superiores
> Profesor Titular                                       de Monterrey
> Campus - Toluca
> Dir. del Depto. de Ciencias Básicas       Cien mts. al nte. de San
> Antonio Buenavista
> Tel(72)741174,741128 ext.2175           Toluca Edo. de México C. P.
> 50252
> Fax(72)741178
> Internet:jortiz at campus.tol.itesm.mx
>                 http:/www.tol.itesm.mx/~amercado/dic/deptos/deptos.html
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


First off, x=4 is not a function. Functions, by definition are single
valued with respect to their argument.   If you want to plot a vertical
line at x=4 try making a function like:

f[x_]:=If[x==4,1000,0].  This may not work well on some plots because it
has an infinitely small non-zero range, so you may want to try something
like:

f[x_]:=If[(x>4-delta&&x<r+delta),1000,0].

To better define this kind of function, look up the theory of the dirac
delta function.

You can also try plotting:
f[x_]:=10^6 Exp[-10^6 (x-4)^2], which is an approximation to a dirac
delta function.