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I am solving following differential equation using Mathematica,

s = NDSolve[{u''[x] == (42/10)*Sin[x]*Sin[x]*u[x], u[-3] == 0, 
   u'[3] == 1}, u, {x, -3, 3}, WorkingPrecision -> 22, 
  InterpolationOrder -> All]
Plot[Evaluate[{u[x] /. s}, {x, -3, 3}], AxesLabel -> {"x", "v(x)"}, 
 PlotStyle -> {Thickness[0.005]}, PlotRange -> All]

I would like to plot this output with gnuplot (as all of the other figure in my report are generated using gnuplot) to be consistent. How can I generate file with $x$ and $u(x)$ values written in 2 columns?

I tried to write output in a file,

  sW = OpenWrite["out.dat", FormatType -> TraditionalForm];
    $Output = {sW};
    Write[sW, x, Evaluate[u[x] /. s], {x, -3, 3, 1}]
    Close[sW];

But this does not print values of $u(x)$

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  • $\begingroup$ You can grab the actual points used by Plot with Cases[plot, _Line, Infinity][[1, 1]]. BTW, not part of your question, but you should use Export instead of raw Open/Write operations. $\endgroup$
    – george2079
    Sep 11, 2014 at 17:46
  • $\begingroup$ Have you seen this question? $\endgroup$
    – Albert Retey
    Sep 11, 2014 at 21:35

1 Answer 1

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After solving your DE, do Table[{x, u[x]} /. %, {x, -3, 3, 0.01}] and save the output to a file "u.dat", which should make it a double column table.

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