       RE: Simple Differentiation?

• To: mathgroup at smc.vnet.net
• Subject: [mg46023] RE: [mg46014] Simple Differentiation?
• From: "sabrina casagrande" <sabrinacasagrande at hotmail.com>
• Date: Tue, 3 Feb 2004 03:20:53 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

```I'm not very confident with Math ematica. I'm learning now for College purpose...
Anyway, I think it's a little bug in your code. Let's explain... When you define
f[x_]+g[x_]^:=1, you are saying to mathematica that when it find f[x_]+g[x_], it must
replace it with 1. so the derivatives of a costant is zero.
I think so. If I'm wrong, let me know.
ciao
sabbri

From: "Sunil Pinnamaneni" <PINNAMA at CIMS.NYU.EDU>
To: mathgroup at smc.vnet.net
To: mathgroup at smc.vnet.net
Subject: [mg46023] [mg46014] Simple Differentiation?
Date: Mon, 2 Feb 2004 05:21:28 -0500 (EST)

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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