Re: Functions of Functions
- To: mathgroup at smc.vnet.net
- Subject: [mg49637] Re: [mg49598] Functions of Functions
- From: DrBob <drbob at bigfoot.com>
- Date: Sun, 25 Jul 2004 02:55:46 -0400 (EDT)
- References: <200407240747.DAA05846@smc.vnet.net>
- Reply-to: drbob at bigfoot.com
- Sender: owner-wri-mathgroup at wolfram.com
Here's your code again: Clear[a, b, c, x] a[x_] := Sin[x] + x^3/2 c = b[a] c[x] It's clear that you've defined a to be a function. A named pattern (x_) is used on both sides of the SetDelayed. But you didn't do anything like that in defining c; no named patterns at all. So how can anyone know what you want c[x] to be? If I could guess, I'd show you how to accomplish it. Slightly more subtle is the point that, as you've defined it, a isn't a function of x; a[x] is. a[y] is a function of y, a[z] depends on z, et cetera. But a isn't a function at all, except when it's given an argument. That's why, once again, there's no mention of x in your definition of c. Bobby On Sat, 24 Jul 2004 03:47:29 -0400 (EDT), Michael J Person <mjperson at mit.edu> wrote: > Hello, > > I was wondering if anyone could help me with this. > > I've gone through the book and help files as best I can, but > can't seem to figure out why the following doesn't work: > > I'm trying to work with functions that take functions > as parameters and return other functions. > > Below is an example... > > (*clear stuff*) > Clear[a, b, c, x] > > > (*Define a functions a*) > \!\(a[x_] := \((Sin[x] + x\^3\/2)\)\) > > > (*define a function of functions*) > \!\(b[f_] = \((f'' + \(3\ f'\)\/2 + 5 f)\)\) > > (*apply the functional function to a*) > c = b[a] > > (*Try to apply the resulting function to something*) > c[x] > > This last step never gives me the results I'd expect by applying > the derivatives of a to x... > > Can anyone tell me where I've gone horribly wrong? > > Thanks much, > > MJ Person > mjperson at mit.edu > > > -- DrBob at bigfoot.com www.eclecticdreams.net
- References:
- Functions of Functions
- From: mjperson@mit.edu (Michael J Person)
- Functions of Functions