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MathGroup Archive 2005

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Re: intersection point from listplots

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55632] Re: intersection point from listplots
  • From: Bill Rowe <readnewsciv at earthlink.net>
  • Date: Thu, 31 Mar 2005 01:25:38 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

On 3/30/05 at 3:21 AM, TMA at nus.edu.sg (Tun Myint Aung) wrote:

>I have two sets of lists for two curves. I can plot using ListPlot.
>What I want to know is how to get the intersection point in
>Mathematica. Any idea!

One approach would be to use Interpolation to create an interpolating function for each list then use FindRoot

For example,

g = Interpolation[Table[x^2, {x, -5, 5}]]; 
f = Interpolation[Table[(x + 2)^2, {x, -5, 5}]]; 
FindRoot[f[x] == g[x], {x, 4}]

{x -> 5.}

Or if the list is n X 2

g = Interpolation[Table[{x, x^2},{x, -5, 5}]]; 
f = Interpolation[Table[{x, (x + 2)^2},{x, -5, 5}]]; 
FindRoot[f[x] == g[x], {x, 0}]

{x -> -1.}
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