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Groups > comp.soft-sys.math.mathematica > #1615

Re: How to plot derivative directly?

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On 4/11/2011 7:05 AM, =8Aer=FDch Jakub wrote:
> Dear mathgroup,
>
> it seems to me, that response to my question shall be very simple,
> but I cannot find it. :-(
>
> I want to plot the derivative of the function. I would like to do it
> directly, something like:
>
> Plot[D[x^3 - 6 (x + 1)^2 + x - 7, x],{x,-3,8}]
>
> It returns: General::ivar: "-2.99978 is not a valid variable."
>
> I can understand that it is because local variable x from Plot command
> interferes with the x variable from the D[].
>
> Yes I can bypass the problem by:
> deriv = D[x^3 - 6 (x + 1)^2 + x - 7, x]
> Plot[deriv, {x, -3, 8}]
>
> which is fully functional, but as far as I know Mathematica, there must
> be some simple solution how to do it directly inside the Plot[].
>
> Thanks in advance for kick-off

Well, you can do this:

Plot[Evaluate[D[x^3 - 6 (x + 1) 2 + x - 7, x]], {x, -3, 8}]


But I think it's worth defining your function as a function.

g[x_] := x^3 - 6 (x + 1) 2 + x - 7

Plot[g'[x], {x, -3, 8}]

--
Helen Read
University of Vermont

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Thread

How to plot derivative directly? Šerých Jakub <Serych@panska.cz> - 2011-04-11 11:05 +0000
  Re: How to plot derivative directly? Peter Pein <petsie@dordos.net> - 2011-04-12 09:53 +0000
  Re: How to plot derivative directly? Helen Read <readhpr@gmail.com> - 2011-04-12 09:54 +0000
  Re: How to plot derivative directly? Stefan <wutchamacallit27@gmail.com> - 2011-04-12 09:56 +0000
  Re: How to plot derivative directly? Wolfgang Windsteiger <Wolfgang.Windsteiger@risc.jku.at> - 2011-04-12 09:57 +0000
  Re: How to plot derivative directly? Peter Breitfeld <phbrf@t-online.de> - 2011-04-12 09:58 +0000

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