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MathGroup Archive 2004

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Re: Non-algebraic solution

  • To: mathgroup at
  • Subject: [mg52492] Re: Non-algebraic solution
  • From: Peter Pein <petsie at>
  • Date: Mon, 29 Nov 2004 01:22:45 -0500 (EST)
  • References: <co6h5d$nmp$>
  • Sender: owner-wri-mathgroup at

B.Ravinder wrote:
> Dear all,
> I want to plot the following type of logarithmic equation having
> dependent variable y and independent variable x.
> Log[y/a] + b*Log[c+y/d] = -x 
> where a,b,c and d are some arbitrary constants.
> First I tried to solve the equation for y using Solve function in 
> Mathematica 4.2, but got the following error 
> message:
> Solve:: tdep : 
> The equations appear to involve the variables to be solved 
> for in an essentially non-algebraic way.
> Could someone please guide me as to how do we solve such equation 
> with/without Mathematica.
>                              or
> If possible, how to obtain y vs. x plot in Mathematica without soving them 
> exactly. 
> Waiting for the kind resonse.
> Regards,
> Ravi
I really wonder why nobody got the idea to use ParametricPlot?

ParametricPlot[{-Log[y/a] - b*Log[c+y/d],y},
   {y,y1,y2}(*desired y-Range*), PlotRange->{{x1,x2},{y1,y2}}]

looks simple to me. Did I miss something?

Peter Pein
10245 Berlin

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