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MathGroup Archive 2003

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NSolve and SplineFit

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44117] NSolve and SplineFit
  • From: mizrandir at hotmail.com (Mizrandir)
  • Date: Thu, 23 Oct 2003 07:15:16 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Hello.

I have a list of (x,y) points. They are equally spaced in the x-axis
so I have decided to use SplineFit in order to have a function I can
evaluate in whichever intermediate point I like. Up till there
everything's ok: I can evaluate the function, I can plot it and I can
even use NIntegrate. Here is more or less what I've done:

In[1]:= <<NumericalMath`SplineFit`

In[2]:= fun=SplineFit[{{4.55},{4.98},{25.42},{73.36},{150.85},{260.07}},Cubic];

In[3]:= fun[2.3]
Out[3]= {36.863}

In[4]:= NIntegrate[fun[x][[1]],{x,0,5}]
Out[4]= 376.97

My problem comes when I try to do something like:

NSolve[fun[x] == 50,x] or NSolve[fun[x][[1]] == 50,x]

and Mathematica doesn't allow me to do this.

Any suggestions are welcome, miz.


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