RE: Function argument
- To: mathgroup at smc.vnet.net
- Subject: [mg66977] RE: [mg66953] Function argument
- From: "Ingolf Dahl" <ingolf.dahl at telia.com>
- Date: Tue, 6 Jun 2006 06:27:04 -0400 (EDT)
- Reply-to: <ingolf.dahl at telia.com>
- Sender: owner-wri-mathgroup at wolfram.com
Hi Bonny, Maybe I am missing your point, but it not a good idea to have f[x] as the second argument of g[a,f[x]]. Since we have not told which part of the expression f[x] which is the function, and which part is the argument, we will get into trouble if we substitute f1[f2[x]] as second argument to g. Should it evaluate to f1[a], or to f1[f2[a]]? We also will get into trouble in other cases. For instance, should the expression a x^2 + b x + c be seen as a function of x, or of a, b or c? You could define g[a_, f_] := f[a] if you are not satisfied with the usual notation f[a] or f@a. (What is wrong with these notations?) Then g[Pi, Sin] evaluates to 0. If you have set f[x_] := a x^2 + b x + c then g[1, f] will evaluate to a + b + c . Also g[1, Function[{x}, a x^2 + b x + c]] , g[1, (a #^2 + b # + c) &] , a x^2 + b x + c /. x -> 1 and x=1; a x^2 + b x + c will give this result, and there are surely a number of additional ways. Best regards Ingolf Dahl Sweden -----Original Message----- From: Bonny [mailto:Banerjee at cse.ohio-state.edu] To: mathgroup at smc.vnet.net Subject: [mg66977] [mg66953] Function argument I would like to define a function g that evaluates another function f at a given value. That is, g[a, f[x]] := f[a] For example, I might want the function f[x]=ax^2+bx+c to be evaluated at x=1 and get the result a+b+c. That is, g[1, ax^2+bx+c] should evaluate to a+b+c. Again, I might want the function f[x]=Sin[x] to be evaluated at x=pi and get the result 0. That is, g[pi, Sin[x]] should evaluate to 0. Is there a way to accomplish this in Mathematica? Any help would be appreciated. Thanks, Bonny.