Re: A variable defaulting to a previous variable?

*To*: mathgroup at smc.vnet.net*Subject*: [mg121977] Re: A variable defaulting to a previous variable?*From*: Peter Pein <petsie at dordos.net>*Date*: Fri, 7 Oct 2011 04:51:34 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <j6jpji$mfe$1@smc.vnet.net>

Am 06.10.2011 10:41, schrieb Brentt: > How would one go about making a variable default to a previous variable? > > I would like results like this: > > In[1]= f[x_, y_: x] := x+y; >> In[2]= f[2,3] >> Out[1]= 5 >> In[3]= f[3] >> Out[1]= 6 >> > > > > But, of course, Mathematica won't let me use a previous argument for the > default of the next argument. Is there a way to do this? In[1]:= f[x_, y___] := If[{y} === {}, 2*x, x + y] In[2]:= f[2, 3] Out[2]= 5 In[3]:= f[3] Out[3]= 6