RE: functional notation

• To: mathgroup at smc.vnet.net
• Subject: [mg26051] RE: [mg26034] functional notation
• From: "David Park" <djmp at earthlink.net>
• Date: Sat, 18 Nov 2000 23:08:05 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```Jerry,

I think you have to specify that x is a function of t and not just a symbol
in your first statement. Why not do it this way:

expr = D[f[x[t]], t]
Derivative[1][f][x[t]]*Derivative[1][x][t]

expr /. x -> (Function[t, a*t])
% /. f -> (1/#1 & )
a*Derivative[1][f][a*t]
-(1/(a*t^2))

David Park

> -----Original Message-----
> From: Blimbaum Jerry DLPC [mailto:BlimbaumJE at ncsc.navy.mil]
To: mathgroup at smc.vnet.net
>
> 	When I type in the following 2 lines:
>
>
> 	D[f[x],x]*D[x[t],t];
>
> 	%/.{x->Function[t,at]
>
> 	I get back
>
> 	a * f ' [Function[t, at ] ]   but what I want to get back is   a*f '
> [t]    or    a*f ' [x]
>
> 	I'm trying to do something with just functional notation and I want
> certain derivatives to 'stay as is' once they are computed..I've looked at
> Hold,etc. and dont know how to use them or even if they are the
> correct way
> to go.
>
>
> 	thanks....Jerry Blimbaum   NSWC  Panama City, Fl

```

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