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Message: "Numerical interation converging too slowly"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83207] Message: "Numerical interation converging too slowly"
  • From: "Hoa Bui" <hoabui05 at gmail.com>
  • Date: Thu, 15 Nov 2007 05:33:18 -0500 (EST)

Hi all,

Please help!

I have a list of points:
lst={{0,0.0673209172484956`},{0.003449278068524249`,0.10109827933089396`},{\
0.014031516572727063`,0.19966139796005267`},{0.04649737451028208`,0.\
2870434103185859`}}

I then define a function NN[x] that returns the linearly interpolated
value at x:
linN = Interpolation[lst, InterpolationOrder -> 1];
NN[x_?NumberQ]:=linN[x];

In[17]:=NN[0]
Out[17]=0.0673209

In[18]:=NIntegrate[NN[s],{s,0,0.45}]
Out[18]=0.344713

However, if I want to make the integral a function of the upper limit,
and plot it:
Plot[NIntegrate[NN[s],{s,0,z}],{z,0,0.045}],
I get this message:
"NIntegrate::slwcon: Numerical integration converging too slowly; suspect one \
of the following: singularity, value of the integration being 0, oscillatory \
integrand, or insufficient WorkingPrecision. If your integrand is oscillatory \
try using the option Method->Oscillatory in NIntegrate."

Maybe there's nothing wrong with the result, but I'm not sure. And the
message is annoying, too.
Does anyone know how to make Mathematica do the work without complaining?

I appreciate it.
HB


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