RE: How to define a polyfunction?

*To*: mathgroup at smc.vnet.net*Subject*: [mg27406] RE: [mg27389] How to define a polyfunction?*From*: "Higinio Ramos" <higra at gugu.usal.es>*Date*: Sun, 25 Feb 2001 00:53:29 -0500 (EST)*References*: <200102230733.CAA06963@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

----- Original Message ----- From: liwen liwen <gzgear at yahoo.com> To: mathgroup at smc.vnet.net Subject: [mg27406] [mg27389] How to define a polyfunction? > Dear friend, > How are you!Now I encounter a problem that I > can not solve for a long time . > It can be express simplely as how to define a > polyfunction,for example,a simple polyfunction may be > defined as that: > > Key[t_]:=If[(t>0),1,0]; > > It is easy to define.However,it will be more difficult > when the condition turns more complicate.For instance: > golf=t^2-t; > Key[t_]:=If[(D[golf[t],t]>0),(t^4+t*3),(t^2.5-t)]; > This may be a solution: golf=x^2-x; Key[t_]:=If[(D[golf,x]/.x->t)>0,t^4+t*3,t^2.5-t]; Even you mey plot the function wher it is defined: Plot[Key[t],{t,-1,1}]