Re: How display negative contours with dashed lines?

• To: mathgroup at smc.vnet.net
• Subject: [mg16893] Re: How display negative contours with dashed lines?
• From: Jens-Peer Kuska <v-jkuska>
• Date: Mon, 5 Apr 1999 02:24:27 -0400
• Organization: Wolfram Research, Inc.
• References: <7e1d1b\$bd6@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi David,

it is not so easy as it seems. Here is a quick and dirty solution

MarkNegativeContours[c_ContourGraphics] :=
Module[{z0, z1, cntNo, dz, cpos, csty, cc},
{z0, z1} = Last[PlotRange /. FullOptions[c]];
cntNo = Contours /. FullOptions[c] /. {l_} :> l;
If[! NumericQ[cntNo], cntNo = 10.];
dz = (z1 - z0)/(cntNo + 1);
cpos = Table[z0 + i*dz, {i, 1, Round[cntNo]}];
csty = {If[# < 0., Dashing[{0.02, 0.01}], Dashing[]]} & /@ cpos;
cc = c /. (Contours -> _) :> (Contours -> cpos) /.
(ContourStyle -> _) :> (ContourStyle -> csty);
If[FreeQ[Last[cc], Contours],
cc\[LeftDoubleBracket]2\[RightDoubleBracket] =
Append[cc\[LeftDoubleBracket]2\[RightDoubleBracket],
Contours -> cpos]];
If[FreeQ[Last[cc], ContourStyle],
cc\[LeftDoubleBracket]2\[RightDoubleBracket] =
Append[cc\[LeftDoubleBracket]2\[RightDoubleBracket],
ContourStyle -> csty]
];
cc
]

Hope that helps
Jens

WOOD DAVID M wrote:
>
> Howdy all.
>
>   Despite rooting around like a cyber-pig after Mathematica truffles
> (with DejaNews, AltaVista, and on MathSource), I can find no
> suggestions or even mention of something that I suspect isn't hard to
> do [except for me :)]
>
> I'd like to produce contour plots for which NEGATIVE function values
> are indicated as dashed lines, while other values use solid lines.
>
> Can anyone suggest how I can on-the-fly specify ContourStyle options
> that will display negative contour values (say in ContourPlot or
> ListContourPlot) as *dashed* lines, via (e.g.) Dashing [or in any
> other way]?
>
> Many thanks!
> --
> David M. Wood
> Department of Physics, Colorado School of Mines, Golden, CO 80401
> Phone: (303) 273-3853; Fax: (303) 273-3840
> e-mail: dmwood at physics.Mines.EDU ; NeXTMail welcome

```

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