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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86763] Re: Creating a function that is a derivative of another function??
  • From: dh <dh at metrohm.ch>
  • Date: Thu, 20 Mar 2008 02:56:00 -0500 (EST)
  • References: <frqpr4$55a$1@smc.vnet.net>


Hi Eric,

if you say: dW[0] this is replaced by: D[W[0],0], not exactly what you 

want. But the solution is simple:

dW[t_]= W'[t]

hope this helps, Daniel



Eric wrote:

> I have a function:

> 

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

> 

> I want the derivative of this funtion wrt t as another function.  The following seems like it works:

> 

> dW[t_] := D[W[t], t]

> 

> dW[t]

> a + 2 b t + 3 c t^2

> 

> But something isn't right??

> 

> dW[0]

> General::ivar: 0 is not a valid variable. >>

> (output line has a partial derivative symbol, subscript 0 followed by a 0)

> 

> The description of the General::ivar error isn't help either??

> 

> Any idea what's going on here??  How can I assign the derivative of a function as another funtion?!

> 

> Thanks

> Eric

> 




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