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Evaluation of functions inside Plot
*To*: mathgroup at smc.vnet.net
*Subject*: [mg21993] Evaluation of functions inside Plot
*From*: Hans-Peter Kunzle <HP.Kunzle at UAlberta.ca>
*Date*: Thu, 10 Feb 2000 02:25:36 -0500 (EST)
*Organization*: University of Alberta
*Sender*: owner-wri-mathgroup at wolfram.com
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
Plot3D::plnc:
{Abs[x + y I], Hue[(N[([Pi] + Arg[x + yI])\(2 Pi)]]} is neither a
machine-size real number at {x,y}={-2.,-2.} nor a list of a real number
and a \alid color directive.
This book was written for Mathematica 2, of course, and presumably
the code must have worked then. Has anything changed since then?
I have tried to wrap 'Evaluate' around some of the expressions, but
this had no effect. Since Abs and Arg only work for numerical
arguments I also tried to replace them by explicit expressions in
x and y. But this did not help either.
Any help is appreciated.
Hans
--
H.P. Künzle | Office: (780)492-3798,492-3396
Dept. of Mathematical Sciences | Fax: (780)492-6826
University of Alberta | E-mail: HP.Kunzle at UAlberta.ca
Edmonton, Canada T6G 2G1 | WWW:http://www.math.ualberta.ca/~hpk
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