Re: Creating a function that is a derivative of another function??
- To: mathgroup at smc.vnet.net
- Subject: [mg86737] Re: Creating a function that is a derivative of another function??
- From: Szabolcs Horvát <szhorvat at gmail.com>
- Date: Thu, 20 Mar 2008 02:51:07 -0500 (EST)
- Organization: University of Bergen
- References: <email@example.com>
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 > 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?! > You need to read this tutorial: http://reference.wolfram.com/mathematica/tutorial/ImmediateAndDelayedDefinitions.html The correct solution is dW[t_] = D[W[t],t]