Re: Information about non-symbol heads

*To*: mathgroup at smc.vnet.net*Subject*: [mg6172] Re: [mg6152] Information about non-symbol heads*From*: "C. Woll" <carlw at u.washington.edu>*Date*: Thu, 27 Feb 1997 02:52:17 -0500*Sender*: owner-wri-mathgroup at wolfram.com

On Mon, 24 Feb 1997, James D Hanson wrote: > How can I get Mathematica 3.0 to tell me what it knows about non-symbolic > heads? To explain what I mean, take a look at a symbolic head. I define b > as a function, the function works, and when I ask Mma about it it tells me > the definition. > > In[1]:= > b[x_] := x^2 > > In[2]:= > b[2] > > Out[2]= > 4 > > In[3]:= > ?b > > "Global`b" > > b[x_] := x^2 > > > So far, so good. Now, suppose I want to use a subscripted variable. I > define the function the same way, and it works. > > In[4]:= > \!\(a\_0[x_]\ := \ x^4\) > > In[5]:= > \!\(a\_0[2]\) > > Out[5]= > 16 > > > But now, when I ask about it, Mma replies that my subscripted variable is > not a symbol or a string. > > > In[6]:= > \!\(\(?a\_0\)\) > > \!\(Information::"ssym" \( : \ \) "\!\(a\_0\) is not a symbol or a string."\) > > Out[6]= > \!\(Information[a\_0, LongForm \[Rule] False]\) > > > So, is there any way to get Mma to tell me the information about a_sub_0? > > -- > James D. Hanson ph. (334) 844-5044 > Department of Physics fax (334) 844-4613 > 206 Allison Laboratory > Auburn University, AL 36849-5311 hanson at physics.auburn.edu > > Hi James, Take a look at the FullForm[] of a subscripted variable, and you will see that for example a_0 (using tex notation) is simply Subscript[a,0]. Thus, a_0 is not a symbol, so that Information[] (or ??) won't work on it. On the other hand, the function definition that you created for a_0 is available, it's just stored under Subscript. Thus, try ??Subscript and you'll find your function definition. The only problem is that if you have a lot of subscript definitions, it may be hard to find the one you're interested in. I couldn't think of a way to narrow down the output of ??Subscript to just the function you're interested in. You could also look into the function Definition[]. Carl