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Re: Contourline values

• To: mathgroup at smc.vnet.net
• Subject: [mg19998] Re: Contourline values
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Sat, 25 Sep 1999 02:40:34 -0400
• References: <7se5tl$qrp@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Rita Bijlsma <R.Bijlsma at iri.tudelft.nl> wrote in message
news:7se5tl$qrp at smc.vnet.net...
> Hi!
>
>   I can not find a way to get contourline values in contour plots.
>
>   Can it be done (automatically) ?
>
>                                    Thanks!
>                                             Rita
>
> --
>   .-. || Drs. Rita Bijlsma                 tel: +31-15-2787109
>  /   \|| IRI dept of Radiation Physics     fax: +31-15-2786422
>  |   ||| Delft University of Technology  email: rita at iri.tudelft.nl
>  |   |||_The Netherlands ______________ http://www.iri.tudelft.nl/~rita
>

Rita,

cg = ContourPlot[1/((x - 1)(x + 1)), {x, -2, 2}, {y, 0, 1},
      ContourShading -> False, Contours -> 3];

ContourGraphics[]


Contour graphics stores a matriex of heights - no explicit lines. To get the
lines we convert the contour graphics object to a Graphics object and then
use Cases to gert a list of the result of passing the first point
coordinates for each line to the expression being plotted. Since there may
be, as here, more than one line at the same height, we then use Union to
remove duplicates.

Cases[Graphics[cg],
    Line[{{x_, y_}, ___}] :> (1/((x - 1)(x + 1))),
    Infinity] // Union


Out[28]=
{-10175.9, -10175.9, -7.48556, -7.48556, -1.63844, -1.63844, 1.1247, 1.1247,
\
6.99341, 6.99341}


--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565