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Re: PlotPoints in plot

  • To: mathgroup at
  • Subject: [mg48647] Re: PlotPoints in plot
  • From: V.Cejka at (Vasek)
  • Date: Wed, 9 Jun 2004 04:17:11 -0400 (EDT)
  • References: <16ykpxjjusq0@legacy>
  • Sender: owner-wri-mathgroup at

In 2D Plot PlotPoints option gives starting number of points in the
plot, but if mathematica sees it is not enough for good evaluation, it
adds more points.
Try Plot[Print[x]; Sqrt[1 - x^2], {x, -1, 1}, PlotPoints -> 3] to see
all evaluations.
You can use PlotDivision option to set max. number of subdivisions
between initial points, but value 0 is not valid and it won´t help you
in this case.

Probably the easiest solution is to generate partially linear function
(like Plot[(-x + 17/2)UnitStep[x - 5] + (x - 3/2)(1 - UnitStep[x -
5]), {x, 0, 10}])
or use Show[Graphics[{Line[{{0, 0}, {1, 1}, {2, 0}}]}], Axes -> True]

On 2 Jun 04 10:51:44 -0400 (EDT), G.L.Narasimham wrote:
>For the plot command  Plot[Sqrt[1-x^2],{x,-1,1},PlotPoints->3]
>I expected to see a triangle joining 3 points on a circle, but a
>continuous line ( default PlotPoints->20? )appears. However,
>gives a triangle. How to get a polygon of straight sides in the
>unparametered Plot?

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