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MathGroup Archive 1997

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Re: FindRoot

  • To: mathgroup at
  • Subject: [mg8928] Re: [mg8887] FindRoot
  • From: David Withoff <withoff>
  • Date: Sat, 4 Oct 1997 22:08:06 -0400
  • Sender: owner-wri-mathgroup at

> I need to plot the root of a transcendental equation
> sin(x)=x/a,     for a from 2 to 3.
> I can find the root for each a using FindRoot. But how do I make a
> continuous plot
> using FindRoot?
> Thanks a lot!
> David Djajaputra

Here are a couple of possible ways to do this:

In[1]:= f[a_] := Module[{x}, x /. FindRoot[Sin[x] == x/a, {x, 2}]]

In[2]:= Plot[f[a], {a, 2, 3}]

Out[2]= -Graphics-

In[3]:= << Graphics`ImplicitPlot`

In[4]:= ImplicitPlot[Sin[x] == x/a, {a, 2, 3}, {x, 1.5, 2.5}]

Out[4]= -ContourGraphics-

This equation has three solutions in this range.  I chose the parameters
in these inputs to pick out one of those solutions.

Dave Withoff
Wolfram Research

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