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MathGroup Archive 1998

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RE: calculation



Try this:
First define a function to help investigate the behaviour of your
equation: f[R_]=.001422409738*R^(73/80)*(R^(1/2)-1)^(-13/40) - .04 Plot
the function (I used Re because for R<0 f is complex) with different
ranges for R:
Plot[Evaluate@Re@f[R],{R,50,100}]
After three tests, the range {R,50,100} seems to lead to something, you
can then use
FindRoot[f[R]==0,{R,80}]
where 80 is a starting value.
{R\[Rule]81.2654929724756414`}
Of course, this is a numerical solving only: you have no garantee of
other roots, and no symbolic expression. But your data seems numerical,
isn't it?

Hope this helps


**************************************** Jean-Marie THOMAS
Conseil et Audit en Inginierie de Calcul Strasbourg, France
****************************************

-----Original Message-----
From: Saeed Esmaily Rashid [mailto:saeedr@stud.ntnu.no] To:
mathgroup@smc.vnet.net
Subject: [mg12030] [mg11966] [mg11966] calculation


Hello!

My name is Saeed and i'm studying physics. I have a problem which ihope
someone can help me with it. I have an equation

.001422409738*R^(73/80)*(R^(1/2)-1)^(-13/40) == .04

i'm using the Solve function in Mathematica 3.0 to solve it for R, but
it calculats endlessly and takes very long time. the question is that
is there any way to optimize this equation or using another function in
Mathematica 3.0 to make it faster to calculate?

Regards





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