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MathGroup Archive 2007

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Re: Plotting two functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg78340] Re: Plotting two functions
  • From: dh <dh at metrohm.ch>
  • Date: Thu, 28 Jun 2007 06:28:54 -0400 (EDT)
  • References: <f5vsai$kr6$1@smc.vnet.net>


Hi,

if I understand correctly, you can numerically calculate X as a function 

of r and you would like to get the inverse r[X]?

The simplest solution is to solve your original equation for r. This 

gives: X->(-gamma r-Pp r-beta r^3-Pp r^3-r^5)/(c+delta r^2+alpha r^4)

You can also do it numerically. Calculate some {X,r} pairs covering the 

region needed, then feed it e.g. to Interpolation to get r[X].

hope this helps, Daniel





SK wrote:

> Hi

> 

> I have a 5th order equation of the form

> 

> eqntony445=r^5+(alpha*X)*r^4+(beta+Pp)*r^3+(delta*X)*r^2+(gamma+Pp)*r

> +c*X==0

> 

> where alpha, beta, delta and gamma are other combination of terms that

> I havent included for the sake of simplicity.

> 

> I can plot X with respect to r for various values of Pp

> 

> Plot[Evaluate[Table[X /. Flatten[Solve[eqntony445 == 0, X]], {Pp, 0,

> 20, 5}]], {r, -0.5, 0.5}]

> 

> The problem is I have another function of the form

> 

> V=Integrate[ ((Pp)/(s)*((r^3+r)/(r^2+1)^2)+2*r,X]

> 

> and need to plot it with respect to X. It keeps spitting out stuff of

> the form Root, which is understandable for 5th order equations, but I

> find that if I can plot V with respect to r then there must be a way I

> can take those r values and translate them to X values. Any help will

> be greatly appreciated.

> Thanks

> S

> 

> 




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