Re: how can I solve a function Erfc

• To: mathgroup at smc.vnet.net
• Subject: [mg48445] Re: how can I solve a function Erfc
• From: "David W. Cantrell" <DWCantrell at sigmaxi.org>
• Date: Sun, 30 May 2004 06:12:06 -0400 (EDT)
• References: <c99d7f\$k3b\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```"Florian Jaccard" <florian.jaccard at eiaj.ch> wrote:
[snip]
> In[9]:= L/(4*(Dg*t)^(1/2)) == InverseErfc[0.9]
>
> In[10]:= Solve[{%, Dg == 5*10^5}, t]

My question now is: Since [2] (using 0.9) works,
why does [1] (using 9/10 instead) fail?

In[1]:= Solve[L/(4*(Dg*t)^(1/2)) == InverseErfc[9/10], t]

Out[1]= {}

In[2]:= Solve[L/(4*(Dg*t)^(1/2)) == InverseErfc[0.9], t]

Out[2]= {{t -> (7.916014709627096*L^2)/Dg}}

Surely [1] indicates a bug of some sort.

David Cantrell

> -----Message d'origine-----
> De : aude [mailto:montgermont.aude at ec-lille.fr]
> Envoyé : vendredi, 28. mai 2004 06:50
> À : mathgroup at smc.vnet.net
> Objet :  how can I solve a function Erfc
>
> 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.

```

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