Re: Limiting range of variables when defining funxtions of several

*To*: mathgroup at smc.vnet.net*Subject*: [mg74707] Re: Limiting range of variables when defining funxtions of several*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Sun, 1 Apr 2007 04:18:43 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <eukv3v$3hr$1@smc.vnet.net>

Michelasso wrote: > Hello everybody, > my problem is that I would like to plot a 3d graphic of a function of > two variables, restricted to domain D={(x,y): x>= 0, y>=0, y <= 1-x}. > > I thought to define the function in this way: > test[x_,y_/; y <= 1-x]:= x+y > > but this seems not to work, while it works for functions of one > variable, i.e.: > test2[x_/; x<= 1]:= 3x > > So, am I doing some syntax error, or is there some other kind of > problems with my definition? You should use the Boole function [1] to define a function over a region. For instance, In[1]:= Clear[test] test[x_, y_] := (x + y)*Boole[x >= 0 && y >= 0 && y <= 1 - x] Plot3D[test[x, y], {x, -2, 2}, {y, -2, 2}]; [...graphic deleted...] Regards, Jean-Marc [1] http://documents.wolfram.com/mathematica/functions/Boole [2] _The Mathematica Book_, "3.5.9 Integrals over Regions", http://documents.wolfram.com/mathematica/book/section-3.5.9