RE: non integer exponents in ContourPlot[]?

*To*: mathgroup at smc.vnet.net*Subject*: [mg35230] RE: [mg35209] non integer exponents in ContourPlot[]?*From*: "David Park" <djmp at earthlink.net>*Date*: Wed, 3 Jul 2002 05:13:36 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Rob, Your function is complex for negative values of x or y when the exponent is not 2. a = -5.75; b = 2; d = 1.1; f[exp1_][x_, y_] := a*((x^exp1 + y^exp1)^0.5 + b*y^exp1) Table[f[2.001][x, 0], {x, -1, 1, 0.25}] // InputForm {-5.749992906223295 - 0.009032075164776287*I, -4.311874410575174 - 0.006773082056369065*I, -2.8740002279114947 - 0.00451447271421603*I, -1.4365021739584314 - 0.002256454194145964*I, 0., -1.4365039461737756, -2.874003773570802, -4.311879730142475, -5.75} If you confine yourself to positive values you will obtain a contour plot. ContourPlot[a*((x^2.001 + y^2.001)^0.5 + b*y^2.0), {x, 0, d}, {y, 0, d}, ContourShading -> False, Contours -> {-6, -3, -1}, PlotPoints -> 30]; I don't know if that is good enough. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ > From: 1.156 [mailto:rob at piovere.com] To: mathgroup at smc.vnet.net > > > Mathematica wizards all: > > The following code runs fine, note the (apparent) floating point > form of the exponents. > > a=-5.75;b=2;d=1.1; > > ContourPlot[a*((x^2.0 + y^2.0)^0.5 + b*y^2.0), {x, -d, d}, {y, > -d, d}, ContourShading -> False, > Contours -> {-6, -3, -1}, PlotPoints -> 30]; > > But, if I make any of the 2.0 exponents say, 2.1, I get big error > messages like > > ContourGraphics::ctpnt: > The contour is attempting to traverse a cell in which some of > the points have not evaluated to numbers, > and it will be dropped. > > However, it works fine if I change the 0.5 exponent to say, 0.55. > > Can anyone give me a hint of what's going on here? I'd sure like > to be able to play with these exponents to fit some data. > > Thanks, Rob > >