Re: extracting contour points
- To: mathgroup at smc.vnet.net
- Subject: [mg92482] Re: extracting contour points
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Wed, 1 Oct 2008 18:32:24 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <gbulri$ld4$1@smc.vnet.net>
peterp wrote:
> I've searched the group but I still have a problem. The contour sought
> below returns two lines (you can actually see them on the graphic output).
> The commands after the contour plot only extract the coordinates of one
> of the two lines. How do I get the second ?
The code you have posted does not work at all, because:
. There are syntax errors
. Erroneous level specification
. When all the above have been corrected, Mathematica still counts only
one Line
> I tried replacing "First" by "Second" but no dice.
:-) Use *Part* (shortcut [[ ]]
> Thanks,
> Peter
>
> f[p_, a_, x_] = - p x + x^(a + 1)
>
> contour =
> ContourPlot[Arg[f[1, .6, x + I y]], {x, -2, 2}, {y, -2, 2}, Contours
> -> {0},
> ContourShading -> False, PlotPoints -> 100]
>
> grcontour = Graphics[contour];
> InputForm[grcontour];
> lns = First[
> Cases[First[grcontour] // Normal, Line[pts_] -> pts, \
> [Infinity]]];
==^^^^^^^^^^
Syntax error: curly braces are required here: {Infinity}
Second error: to find the head Line, you must start from level zero,
i.e. {0, Infinity}
> dat = Table[lns];
=============^^^^^^
Syntax error: Table requires two operands, the second being an iterator.
> Export["junk.dat", Re[dat]]
>
In[1]:= f[p_, a_, x_] := (-p)*x + x^(a + 1)
contour =
ContourPlot[Arg[f[1, 0.6, x + I*y]], {x, -2, 2}, {y, -2, 2},
Contours -> {0}, ContourShading -> False]
grcontour = Graphics[contour];
lns = Cases[Normal[First[grcontour]],
Line[pts_] -> pts, {0, Infinity}][[1]];
Count[Normal[grcontour], _Line, {0, Infinity}]
Out[5]= 1
In[6]:= contour =
ContourPlot[Arg[f[1, 0.6, x + I*y]], {x, -2, 2}, {y, -2, 2},
Contours -> {0, 1}, ContourShading -> False]
grcontour = Graphics[contour];
lns = Cases[Normal[First[grcontour]],
Line[pts_] -> pts, {0, Infinity}][[1, 2]];
Length[lns]
Count[Normal[grcontour], _Line, {0, Infinity}]
Out[9]= 2
Out[10]= 3
HTH,
-- Jean-Marc