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Re: Get list of function variables?

• To: mathgroup at smc.vnet.net
• Subject: [mg84082] Re: Get list of function variables?
• From: David Bailey <dave at Remove_Thisdbailey.co.uk>
• Date: Mon, 10 Dec 2007 04:29:56 -0500 (EST)
• References: <fhjs5v$4t3$1@smc.vnet.net> <fhu7j5$7b1$1@smc.vnet.net> <fi3jvl$bqs$1@smc.vnet.net>

Jason Quinn wrote:
> On Nov 21, 6:09 am, Szabolcs <szhor... at gmail.com> wrote:
>> It seems that you were not convinced by the previous posts that the
>> original question does not really make sense in Mathematica (because
>> there are no "function variables", or "functions", only patterns and
>> transformation rules, and the pattern names don't carry any
>> information by themselves).  So here is an example of a mathematical
>> function, implemented in Mathematica, on which getVariables[] does not
>> work:
>>
>> factorial[0] = 1
>> factorial[n_] := n factorial[n-1]
>>
>> May I ask what you intend to use getVariables[] for?
> 
> I am aware that the "solutions" I posted do not hold in general. My
> basic desire for the getVariables function was to help generate a new
> function with those variables (and another set of the same size). I
> wanted a notebook that could give the the error function for ANY
> function the user inputed without having to do any work. Maybe there's
> a better way than how I did it (but I have a working notebook so I'm
> better off than I was).
> 
> In other words give some function, say, the price to carpet an "x" by
> "y" by "z" room at "w" per square unit area:
> f(w,x,y,z)=w(x*y*z)
> I want the sigma error on f given sigma errors on the variables. So a
> new function "ef"
> ef(x,y,z,ex,ey,ez)
> where ef is defined by the usual error propagation equation a sum over
> partial derivatives squared. The "e" prefix denotes the sigma error on
> the corresponding variable. Note the new function recognizes w as a
> parameter.
> 
> If I went about this in some ass-backwards fashion by grabbing the
> variables from f directly, I'm a little bit embarrassed but would be
> interested in knowing a better way.
> 
> Jason
> 
> 
> 
> 
> 
> 
> 
> 
> 
I don't really know what you want your getVariables function for, but if 
you type the name of a built-in function - say Plot - and then press 
Ctrl-Shift-K (under Windows), you get some help with the arguments. This 
also seems to work with user-defined functions if they have a suitable 
usage statement.

David Bailey
http://www.dbaileyconsultancy.co.uk