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Re: Solve::nsmet

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  • Subject: [mg121411] Re: Solve::nsmet
  • From: Bill Rowe <readnews at>
  • Date: Wed, 14 Sep 2011 05:14:29 -0400 (EDT)
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On 9/13/11 at 7:18 AM, diviya.smith at (Diviya Smith) wrote:

>I am trying to solve this equation using Mathematica but I keep
>getting the following error "Solve::nsmet: This system cannot be
>solved with the methods available to Solve".

>Solve[(p*(1 - e^(-x*(d - p))))/((-d + p) (1 - e^(x*p))) == y, x]

>I have also tried *Reduce* but that does not work either. Any
>suggestions, how I can fix the error? I am new to
>apologies if this is a very basic question.

Your equation does not appear to have any closed form solution.
Your only recourse would be to specify values for p,d and then
use Solve or numeric methods. At least there are some specific
values you can give p,d and y which Solve can deal with. For example

In[24]:= eq = (p*(1 - E^(-x*(d - p))))/((-d + p) (1 - E^(x*p))) ==
     y /. {p -> 2, d -> 1, y -> 1/2};

In[25]:= Solve[eq, x]

Out[25]= {{x->log(3)}}

But I suspect one could easily find values that would either
have no solution or would not allow Solve to find a solution.

Note, I have assumed your e was intended to be E. If this is not
the case Solve can still find a solution. And you could leave y
unspecified, that is:

In[33]:= eq = (p*(1 - e^(-x*(d - p))))/((-d + p) (1 - e^(x*p))) ==
     y /. {p -> 2, d -> 1};

In[34]:= Solve[eq, x]

Out[34]= {{x -> Log[-((y - 2)/y)]/Log[e]}}

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