Re: Evaluation of functions inside Plot
- To: mathgroup at smc.vnet.net
- Subject: [mg22060] Re: Evaluation of functions inside Plot
- From: Daniel Duque Campayo <campayo at phys.washington.edu>
- Date: Fri, 11 Feb 2000 02:38:45 -0500 (EST)
- Organization: University of Washington
- References: <87tpki$5iq@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hans-Peter Kunzle wrote:
>
> I still do not understand well enough how expressions get
> evaluated inside a Plot or similar functions (NDSolve etc.).
>
> This time I copied the code directly from the (quite old)
> book by T.W. Gray and J. Glynn, Exploring Mathematics with
> Mathematica (p.142):
>
> Plot3D[
> { Abs[x+y I], Hue[ N[(Pi+Arg[x + yI]) /(2 Pi)]]},
> {x,-2,2},{y,-2,2}],
> AxesLabel->{"Re","Im","Abs[z]"},PlotPoints->15
> ];
>
> This produces several error messages
Yes, because it should be "y I" in the Arg[], with a space in between.
Mathematica thinks yI is a new (undefined) variable.
Also, you have an extra bracket. So the thing should be
Plot3D[
{ Abs[x+y I], Hue[ N[(Pi+Arg[x + y I]) /(2 Pi)]]},
{x,-2,2},{y,-2,2},
AxesLabel->{"Re","Im","Abs[z]"},PlotPoints->15
];
Regards
Dani
PS: About the Evaluate[] thing, I don't understand it so much; it
tipically use it when things go slow and it usually speeds them up.
--
Daniel Duque
Dpt. of Physics
University of Washington
Seattle, WA 98195, USA