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From: Tonja Krueger on 5 Aug 2010 07:32
I want to rearrange the equation below so that it would look like:
x-> ....
I tried:
Solve[G==-(Sqrt[\[Pi]/2]*Erfc[x]*(-\[Mu]+Log[x]))/(2*Sqrt[\[Pi]]*\[Sigma]),x]
But then I got the error message:
Solve::tdep: The equations appear to involve the variables to be solved for in an essentially non-algebraic way.
Is there a way to solve the equation?
Thanks Tonja
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From: Bob Hanlon on 6 Aug 2010 06:57
I believe that you will have to use numeric techniques

Manipulate[
FindRoot[
G == (Erfc[x]*(\[Mu] - Log[x]))/(2*Sqrt[2]*\[Sigma]),
{x, 1}] // Chop,
{{\[Mu], 0}, 0, 2.25, Appearance -> "Labeled"},
{{\[Sigma], 1}, .1, 5, Appearance -> "Labeled"},
{{G, 0}, 0, 4, Appearance -> "Labeled"}]


Bob Hanlon

---- Tonja Krueger <tonja.krueger(a)web.de> wrote:

=============
I want to rearrange the equation below so that it would look like:
x-> ....
I tried:
Solve[G==-(Sqrt[\[Pi]/2]*Erfc[x]*(-\[Mu]+Log[x]))/(2*Sqrt[\[Pi]]*\[Sigma]),x]
But then I got the error message:
Solve::tdep: The equations appear to involve the variables to be solved for in an essentially non-algebraic way.
Is there a way to solve the equation?
Thanks Tonja



From: Bill Rowe on 6 Aug 2010 06:57
On 8/5/10 at 7:32 AM, tonja.krueger(a)web.de (Tonja Krueger) wrote:

>I want to rearrange the equation below so that it would look like:
>x-> .... I tried:
>Solve[G==-(Sqrt[\[Pi]/2]*Erfc[x]*(-\[Mu]+Log[x]))/(2*Sqrt[\[Pi]]*\[
>Sigma]),x] But then I got the error message: Solve::tdep: The
>equations appear to involve the variables to be solved for in an
>essentially non-algebraic way. Is there a way to solve the equation?

There is no closed form symbolic solution for that equation. You
can find numeric solutions using FindRoot after given G, \[Mu]
and \[Sigma] numeric values. For example:

In[6]:= FindRoot[1 + Erfc[x] Log[x]/(2 Sqrt[2]), {x, .001, 10}]

Out[6]= {x->0.0499295}

Here, I've set G = \[Sigma] = 1 and \[Mu] = 0


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