Re: What is the difference between z[x_]:= D[y[x],x] and z[x_]:=y'[x]?

• To: mathgroup at smc.vnet.net
• Subject: [mg27462] Re: [mg27436] What is the difference between z[x_]:= D[y[x],x] and z[x_]:=y'[x]?
• From: BobHanlon at aol.com
• Date: Mon, 26 Feb 2001 01:29:28 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Look at what is stored under the different definitions and how the different
definitions respond to numeric input.

Clear[z];
z[x_] = D[y[x],x];
?z
z[5]

Clear[z];
z[x_]:= D[y[x],x];
?z
z[5]

Clear[z];
z[x_]:= Evaluate[D[y[x],x]];
?z
z[5]

Clear[z];
z[x_]:=y'[x];
?z
z[5]

Clear[z];
z[x_] =y'[x];
?z
z[5]

You always have to make sure that the derivative is taken before a numerical
substitution occurs with its variable of differentiation.

Bob Hanlon

In a message dated 2001/2/25 9:30:45 PM, gzgear at yahoo.com writes:

>I want to know the difference between z[x_]:=
>D[y[x],x] and z[x_]:=y'[x].
>

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