Re: problems with the definition of a function

*To*: mathgroup at smc.vnet.net*Subject*: [mg36668] Re: [mg36651] problems with the definition of a function*From*: Murray Eisenberg <murraye at attbi.com>*Date*: Wed, 18 Sep 2002 02:09:56 -0400 (EDT)*Organization*: Mathematics & Statistics, Univ. of Mass./Amherst*References*: <200209160434.AAA07065@smc.vnet.net>*Reply-to*: murray at math.umass.edu*Sender*: owner-wri-mathgroup at wolfram.com

The same principles that allow particular cases for defining a function of a single variable would apply here, because Mathematica applies particular rules before it applies general ones. For example: f[0, y_] := 0 f[2 Pi, y_] := y - 2 f[4 Pi, y_] := y - 4 f[x_, y_] := x^2 + y^3 This will do exactly what it looks like it does! If you have a general family of particular cases, say at all even integral multiples of Pi, then you could use something like the following in place of the first three lines above: f[k_ Pi, y_] := y - k /; IntegerQ[k] && EvenQ[k] There are variants as to where to place the "condition" IntegerQ[k] && EvenQ[k], for example: f[k_ Pi , y_] /; IntegerQ[k] && EvenQ[k] := y - k f[k_ Pi /; IntegerQ[k] && EvenQ[k], y_] := y - k fabio bagarello wrote: > Hi there!! > I have quite an easy and annoying problem with mathematica: > I need to define a function f(x,y) which takes some values for > x=0,2pi,4pi (indepently of y) and has a different expression for all > the other values of y. This is easily done for one-dimensional > functions but I am in serious troubles for my two-dimensional problem: > any suggestion? > Thanks a lot, > Fabio > > > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street Amherst, MA 01375