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

• To: mathgroup at smc.vnet.net
• Subject: [mg86745] Re: Creating a function that is a derivative of another function??
• From: "David Park" <djmpark at comcast.net>
• Date: Thu, 20 Mar 2008 02:52:38 -0500 (EST)
• References: <frqpr4\$55a\$1@smc.vnet.net>

```When Mathematica evaluates your dW statement with 0 it uses D[W[0],0], which
makes no sense for the D statement. Use the Derivative construction.

W[t_] := a t + b t^2 + c t^3
dW[t_] := Derivative[1][W][t]

dW[t]
a + 2 b t + 3 c t^2

dW[0]
a

--
David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/

"Eric" <eric.r.george at aero.org> wrote in message
news:frqpr4\$55a\$1 at smc.vnet.net...
>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
>

```

• Prev by Date: Re: Creating a function that is a derivative of another function??
• Next by Date: Re: Exceptions Style Problem
• Previous by thread: Re: Creating a function that is a derivative of another function??
• Next by thread: Mathematica hangs...