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MathGroup Archive 2004

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Re: how can I solve a function Erfc

  • To: mathgroup at smc.vnet.net
  • Subject: [mg48442] Re: how can I solve a function Erfc
  • From: DrBob <drbob at bigfoot.com>
  • Date: Sun, 30 May 2004 06:12:03 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I've used Solve below, but I had to do a couple of steps manually, first.

Erfc[L/(4*(Dg*t)^(1/2))] == 9/10;
%[[1,1]] == InverseErfc[Last[%]];
(#1^(-2) & ) /@ %;
Solve[%, t];
f[L_, Dg_] = t /. First[%]

L^2/(16*Dg*InverseErf[Infinity, -(9/10)]^2)

Plot[f[ell, 5*10^5], {ell, -10, 10}];

I wonder why Solve can't deal with the original equation?

Bobby

From: aude (montgermont.aude at ec-lille.fr)
To: mathgroup at smc.vnet.net
Subject: [mg48442] how can I solve a function Erfc

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Hi,

I have to solve this function:

Erfc[L/(4*(Dg*t)^(1/2))]= 0.9

Dg is constant.

Dg=5*10^5

I want to plot t as a function of L.

thanks.

aude


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