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Re: Creating a function that is a derivative of another function??

• To: mathgroup at smc.vnet.net
• Subject: [mg86743] Re: Creating a function that is a derivative of another function??
• From: Bhuvanesh <lalu_bhatt at yahoo.com>
• Date: Thu, 20 Mar 2008 02:52:15 -0500 (EST)

In your case, dW[0] is trying to compute (more or less) D[a*t + b*t^2 + c*t^3 /. t->0, t /. t->0] == D[0, 0], which naturally gives an error message, since zero is not a valid variable.

Here's one way to do what you want:

In[1]:= W[t_] := a*t + b*t^2 + c*t^3

In[2]:= dW[t0_] := Derivative[1][W][t0]

In[3]:= dW[t] //InputForm

Out[3]//InputForm= a + 2*b*t + 3*c*t^2

In[4]:= dW[0]

Out[4]= a

Bhuvanesh,
Wolfram Research