Re: Plot3D: plot does not display when PlotPoints different from 25. Mathematica 5.2

*To*: mathgroup at smc.vnet.net*Subject*: [mg65824] Re: [mg65730] Plot3D: plot does not display when PlotPoints different from 25. Mathematica 5.2*From*: bsyehuda at gmail.com*Date*: Mon, 17 Apr 2006 02:29:21 -0400 (EDT)*References*: <200604160749.DAA11119@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

I would recommend on changing the way you define the function u[x_,y_]. Which[] is a better way of expressing this function. As for the graphical problem, you are trying to compare to an exact number (0 in your case) while Plot3D has a sampling algorithm which for PlotPoints different from 25 skips this value since it uses approximate values (Machine precision numbers). Therefore, only 0 is returned (the default value of your function). A better way is defining something such as If[Abs[x]<= some small number rather than If[x==0 regards yehuda On 4/16/06, nma at 12000.org <nma at 12000.org> wrote: > > [This post has been delayed due to email problems - moderator] > > > Remove["Global`*"] > > u[x_, y_] := Module[{}, > If[x == 0, Return[1 + y]]; > If[y == 0, Return[1]]; > Return[0]; > ] > > Plot3D[u[x, y], {x, -1, 2}, {y, -1, 2}, > FaceGrids -> None, > AxesLabel -> {"U(x,y)", "x", "y"}, > PlotLabel -> "Boundary conditions", > PlotPoints -> 25] > > works OK. But if you change 25 to say 26 in the last line above, the > plot does not show up any more ! > > Can someone explain why this is? > > thanks, > Nasser Abbasi > >

**References**:**Plot3D: plot does not display when PlotPoints different from 25. Mathematica 5.2***From:*nma@12000.org