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Re: Dumb question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg27780] Re: Dumb question
  • From: Erk Jensen <Erk.Jensen at cern.ch>
  • Date: Sat, 17 Mar 2001 05:41:05 -0500 (EST)
  • Organization: CERN http://www.cern.ch
  • References: <98neji$8g@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Gustavo Seabra wrote:
> 
> Hello. I know this may be a dumb question, and I apologize for doing that.
> But I am new to Mathematica, and I'm having a little trouble with this. I
> want to plot the equation:
> 
> P=[sin(a-x)*t/(a-x)]^2
> 
> with fixed t (say, 1) and fixed a (say, Pi/2), with x varying from 0 to Pi.
> I know there is a discontinuity at x=a. Is there a way to plot this? I mean,
> P(x) versus x?
> 
> Thanks,
> --
> -----------------------------------------------------------------
> Gustavo Seabra - Graduate Student
> Chemistry Department
> Kansas State University
> -----------------------------------------------------------------

1) I see you're new since you're using the wrong type of brackets for
Mathematica. Probably you mean (Sin[(a-x) t]/(a-x))^2 There is no problem to
plot this, since in Plot[f,{variable,min,max}] you can specify which is the
variable for the plot, which are the parameters - in your case you may want to
try
p=(Sin[(a-x) t]/(a-x))^2
Plot[p/.{a->Pi/2,t->1},{x,0,Pi}]

2) You will not see any discontinuity since there is none. There is only a hole,
but the lim from both sides will be the same, so you can fill the hole, e.g.
defining (attn., this is not exactly your expression!)

si[x_ /; x == 0] := 1
si[x_ /; x != 0] := Sin[x]/x

It's exactly like the function x/x which has a hole at x=0 ... -  so what!

Ciao
     -erk-


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