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

*To*: mathgroup at smc.vnet.net*Subject*: [mg65795] Re: Plot3D: plot does not display when PlotPoints different from 25. Mathematica 5.2*From*: Farhat Habib <farhat at hotmail.com>*Date*: Mon, 17 Apr 2006 02:28:51 -0400 (EDT)*Organization*: Ohio State University*References*: <e1stnb$bk7$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

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 > Its because of the way the points are sampled from the range {-1,2}. If x=0, or y=0 aren't one of the points at which Mathematica is sampling the function then the plot will be uniformly zero. If you put PlotPoints->49, e.g., you will se the desired plot. -F