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# Re: Mathematica Plot [help]
Wei Xu wrote:
> I want to draw a surface, say sin[x,y], defined on a triangular domain,
> say, x:[0,1], y:[0,1] and x+y <=1.
> I tried to use the following command:
> ParametricPlot3D[{fx, fy, fz}, {x,0,1}, {y,0,1-x}] but it is not
> allowed to use {y,0,1-x}.
Wei:
Find a parameterization of the region, Rxy, that you wish to plot f[x,y]
over.
{s,t} -> {x[s,t], y[s,t]}
taking a rectangle [smin,smax] x [tmin, tmax] onto R[x,y].
Plot
ParametricPlot3D[{x[s,t],y[s,t],f[x[s,t],y[s,t]},
{s,smin,smax},{t,tmin,tmax}]
For your example take
x[s_,t_] := s
y[s_,t_] := s t
f[x_,y_] := Sin[x y]
ParametricPlot3D[{x[s,t], y[s,t], f[x[s,t],y[s,t]]},{s,0,1}, {t,0,1}]
There are many ways of implementing this idea: here is one using
formulas and replacement.
{x,y,z}/.z->Sin[x y]/.{x->s, y-> s t}
{s, s*t, Sin[s^2*t]}
ParametricPlot3D[%//Evaluate,{s,0,1}, {t,0,1}]
This will work without the use of Evaluate, but less efficiently --
Allan Hayes
Mathematica Training and Consulting
Leicester, UK
hay@haystack.demon.co.uk
http://www.haystack.demon.co.uk
voice: +44 (0)116 271 4198
fax: +44 (0)116 271 8642
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