       Re: Simple Differentiation?

• To: mathgroup at smc.vnet.net
• Subject: [mg46106] Re: Simple Differentiation?
• From: drbob at bigfoot.com (Bobby R. Treat)
• Date: Fri, 6 Feb 2004 04:15:30 -0500 (EST)
• References: <bvla84\$8r\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```I'd do it this way:

f[x_] := 1 - g[x]
D[f[x] + g[x], x]
D[f[x], x] + D[g[x], x]
0
0

Bobby

"Sunil Pinnamaneni" <pinnama at cims.nyu.edu> wrote in message news:<bvla84\$8r\$1 at smc.vnet.net>...
> In Mathematica 5.0, if one types in:
>
> f[x_]+g[x_]^:=1   (1)
>
> and then types
>
> dx(f[x]+g[x])
>
> we get 0.
>
> However, if we type dx(f[x]) + dx(g[x]) after typing (1), we get
>
> f'[x] + g'[x].
>
> Mathematica doesn't recognize that f'[x]+g'[x]=
> dx(f[x]+g[x]), which equals 0. How does one get Mathematica to do this?
>
> I'm interested in more complicated examples, which involve more complex
> differential relations, but I should be able to do things in those
> situations given a nice, natural way of handling this toy case. Though this
> seems like a pretty simple thing, I wasn't able to find any thing in the
> Mathematica Book or elsewhere, which would help with this type of things.
>
> Thanks,
> Sunil

```

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