Re: "UnFullForm"ing an Expression?

*To*: mathgroup at smc.vnet.net*Subject*: [mg13260] Re: [mg13151] "UnFullForm"ing an Expression?*From*: Wouter Meeussen <eu000949 at pophost.eunet.be>*Date*: Fri, 17 Jul 1998 03:17:52 -0400*Sender*: owner-wri-mathgroup at wolfram.com

hi Siegman, my interpretation is: 1/ you used SetDelayed or ":=" in defining f2 this stores: In[12]:= ?f2 "Global`f2" f2[a_, x_] := D[f1[a, x], x] 2/ when you put f2 in a table, and pass numeric values num1 and num2 values for a and x, then this is substituded in the RHS of the definition, resulting in : D[f1[num1, num2], num2] , causing your CPU to ache badly. 3/ curcumvent it with "Evaluate" : In[13]:= Evaluate at f2[a,x] Out[13]=a^2*Cos[x] - a*Sin[x] and so: Table[ Evaluate at f2[a,x],{x,3},{a,3}] or else use a simple "Set" in the definition of f2. wouter. At 07:42 13-07-98 -0400, AES wrote: >I recently posted a query noting that if you enter the following > > f1[a_,x_] :=a Cos[x] + a^2 Sin[x] > > f2[a_,x_] := D[f1[a,x],x] > >you can make a Table[ ] of f1[a,x] but not of f2[a,x]. > >If I look at the FullForms for these, e.g. > > f1[a,x] // FullForm > > f2[a,x] // FullForm > >they both look like simple functions to me (i.e., f2[a,x] shows no >visible memory of having originated from a derivative), except the f2 >is inside a "FullForm[ ]" wrapper and f1 isn't. > >Is there a way to "UnFillForm" f2 ? If so, would f2 from then on act >like f1 ? Does this query make any sense? > >I'd like to understand the situation here. > >Thanks siegman at ee.stanford.edu > > Dr. Wouter L. J. MEEUSSEN w.meeussen.vdmcc at vandemoortele.be eu000949 at pophost.eunet.be