Re: Behaviour of Plot/ListPlot & Export

*To*: mathgroup at smc.vnet.net*Subject*: [mg31771] Re: [mg31722] Behaviour of Plot/ListPlot & Export*From*: BobHanlon at aol.com*Date*: Sat, 1 Dec 2001 02:45:48 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

In a message dated 2001/11/29 3:07:25 AM, steve at fractalus.com writes: >Mathematica 4.1.1.0 on Linux > >If I try > >Plot[Sqrt[Prime[n]/Prime[n + 1]], {n, 1, 100}] > >I get: > >Prime::"intpp": "Positive integer argument expected in \ >\!\(Prime[1.000004125`]\)." >Prime::"intpp": "Positive integer argument expected in \ >\!\(Prime[1.000004125`]\)." >Prime::"intpp": "Positive integer argument expected in \ >Prime[2.0000041250000002`]." > >And a bunch more errors, however if I try > >ListPlot[Table[Sqrt[Prime[n]/Prime[n + 1]], {n, 1, 100}]] > >Then it works fine. Presumably Table[x,{x,1,100}] steps through integers > >while Plot does not. This is surprising, I expected the same behaviour >of them. Is this a bug? Is this documented (I did look around)? > Prime requires its argument to be a positive integer. The PlotPoints used by Plot are generally not integers, for example look at Plot[n,{n,1,100}, DisplayFunction->Identity][[1,1,1,1]] You can restrict the arguments to Prime (1) as you did using ListPlot and a Table, or (2) Round or truncate n. p1 = Plot[Sqrt[Prime[Floor[n]]/Prime[Floor[n+1]]],{n,1,100}]; While the default setting for PlotPoints is 25, the PlotPoints adjust automatically to try and capture detail. The abrupt changes in this plot resulted in many more PlotPoints Length[p1[[1,1,1,1]]] 664 Bob Hanlon Chantilly, VA USA