Re: Contour levels

*To*: mathgroup at smc.vnet.net*Subject*: [mg83817] Re: [mg83766] Contour levels*From*: Bob Hanlon <hanlonr at cox.net>*Date*: Sat, 1 Dec 2007 05:46:04 -0500 (EST)*Reply-to*: hanlonr at cox.net

cplot = ContourPlot[x^2 + y^2, {x, -1, 1}, {y, -1, 1}] data = Cases[First[cplot] // Normal, Line[pts_] -> pts, Infinity]; ListPlot[data, Joined -> True, Frame -> True, Axes -> False, AspectRatio -> Automatic] data2 = Select[data, Abs[Total[#[[1]]^2] - 0.4] < 0.01 &]; ListPlot[data2, Joined -> True, Frame -> True, Axes -> False, AspectRatio -> Automatic] Bob Hanlon ---- sigmundv at gmail.com wrote: > A few days ago a question was posted on how to extract the coordinates > defining each of the contours returned by ContourPlot[]. Then I would > like to ask if there is any way to also get the level they belong to? > Let me illustrate the question by an example: > > If I plot the contours (or level curves) of the scalar function f(x,y) > = x^2 + y^2 by using > > cplot = ContourPlot[x^2+y^2,{x,-1,1},{y,-1,1}] > > in Mathematica 6.0, I get a few circles. The points defining these > circles are extracted as follows: > > Cases[First[cplot] // Normal, Line[pts_] -> pts, Infinity]; > > This returns a few lists, each containing a selection of points on a > circle. Then my question is, if there is any way I can get the level > to which each of these lists belong. That is, can I ask Mathematica > which list of points belongs to f(x,y) = 0.4, for example, or, which > level does a given list of points belong to? > > Kind regards, > Sigmund Vestergaard >