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Re: Plot artifact of NDSolve result

• To: mathgroup at smc.vnet.net
• Subject: [mg116114] Re: Plot artifact of NDSolve result
• From: Oliver Ruebenkoenig <ruebenko at wolfram.com>
• Date: Wed, 2 Feb 2011 07:03:23 -0500 (EST)

On Wed, 2 Feb 2011, Bert RAM Aerts wrote:

> Both in Mathematica 8.0.0 and 7.0.1 the plot of NDSolve result is
> wrong near x-axis point 60. But when zooming in, plot is correct.
>
> Notebook and screenshot of result are available on http://users.skynet.be/fa991376/
>
> eqn4 = y''[t] == -y[t]^2 + t
>
> sol4 = NDSolve[{eqn4, y[0] == 0, y'[0] == 1}, y, {t, 0, 70},
>  WorkingPrecision -> 20, MaxStepSize -> 0.01]
>
> Below plot contains the artifact:
>
> Plot[Evaluate[{y[t], y'[t], y''[t]} /. sol4], {t, 0, 70},
> PlotRange -> All]
>
> Below plot is correct:
>
> Plot[Evaluate[{y[t], y'[t], y''[t]} /. sol4], {t, 50, 70},
> PlotRange -> All]
>
> Is there a way to avoid this?
>
>

You could use

Plot[Evaluate[{y[t], y'[t], y''[t]} /. sol4], {t, 0, 70},
  PlotRange -> All, PlotPoints -> 30]

Oliver