Re: How to plot derivative directly?
- To: mathgroup at smc.vnet.net
- Subject: [mg118113] Re: How to plot derivative directly?
- From: Heike Gramberg <heike.gramberg at gmail.com>
- Date: Tue, 12 Apr 2011 06:53:34 -0400 (EDT)
This has to do with the fact that Plot has attribute HoldAll (you can check this
with Attributes[Plot]). This means that the derivative doesn't get evaluated until
after w has been replaced with numerical values. To overcome this, you need to
tell mathematica to evaluate the derivative before plugging in numbers. This can
be done with evaluate:
Plot[Evaluate[D[x^3 - 6 (x + 1)^2 + x - 7, x]], {x, -3, 8}]
Heike
On 11 Apr 2011, at 12:05, =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
>
> Jakub
>