Re: Indefinite numbers of arguments in a function

*To*: mathgroup at smc.vnet.net*Subject*: [mg87844] Re: Indefinite numbers of arguments in a function*From*: Albert Retey <awnl at arcor.net>*Date*: Fri, 18 Apr 2008 07:10:16 -0400 (EDT)*References*: <fu9fnt$c91$1@smc.vnet.net>

Patrick Klitzke wrote: > Hello everybody, > Is it possible to define a function in Mathematica, where the numbers of > arguments does not matter? > > I know the function Plus is defined like that: > > I call the function with two arguments( for example Plus[5,3]) or I can > call the function with five arguments (for example > Plus[1,6,4,6,8]). > > How can i define a function in Mathematica like that? I know I can > define for ever number of arguments a function like that: > MyPlus[a_,b_]:=a+b > MyPlus[a_,b_,c_]:=a+b+c > MyPlus[a_,b_,c_,d_]:=a+b+c+d > MyPlus[a_,b_,c_,d_,e_]:=a+b+c+d+e > > I also know that I can create a list as one argument: > > MyPlus[list_List] := ( > m = 0; For[n = 1, n < Length[list] + 1, n++, m += list[[n]] ]; > m > ) > > > But since there are functions like Plus, there has to be a way to define > those kind of functions. > > I would be very glad, if someone could give me his advice. > > Best regards, > > Patrick Klitzke > > email: philologos14 at gmx.de Any symbol can have attributes which control how it behaves. The attribute you are looking for is Orderless: In[3]:= SetAttributes[fff,Orderless] In[6]:= fff[1,2,3,4]==fff[2,4,3,1] Out[6]= True How would you know? Check the attributes of Plus and see which fits, if in doubt, look them up in the documentation: In[2]:= Attributes[Plus] Out[2]= {Flat,Listable,NumericFunction,OneIdentity,Orderless,Protected} hth, albert