Mathematica 9 is now available
Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Anomaly? or at least a surprise.

  • To: mathgroup at smc.vnet.net
  • Subject: [mg90265] Re: [mg90250] Anomaly? or at least a surprise.
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Fri, 4 Jul 2008 03:55:43 -0400 (EDT)
  • References: <200807031012.GAA03197@smc.vnet.net>

On 3 Jul 2008, at 19:12, Steve Gray wrote:

> Doing D[ArcTan[x], x] gives 1/(x^2+1) as expected.
> Doing Plot[D[ArcTan[x]],{x,-10,10},PlotRange->Full] with no variable
> to differentiate by gives a correct plot (!) This is surprising - Help
> says nothing about leaving out the independent variable even when the
> function is of only one variable. Now, doing
> Plot[D[ArcTan[x], x], {x, -10, 10}, PlotRange -> Full]
> gives error messages such as
>
> General::ivar: -9.18326 is not a valid variable. >>
> General::ivar: -9.59143 is not a valid variable. >>, etc.
>
> I thought that D[ArcTan[x], x] and 1/(x^2+1) should behave identically
> in the Plot statement.
>
> Is this behavior something I should know? Thank you.
>
> Steve Gray
>

I don't think this

Plot[D[ArcTan[x]],{x,-10,10},PlotRange->Full]

is "the correct plot" of this:

Plot[Evaluate[D[ArcTan[x], x]], {x, -10, 10}, PlotRange -> Full]

Andrzej Kozlowski





  • Prev by Date: Re: Anomaly? or at least a surprise.
  • Next by Date: Re: more inset export problems
  • Previous by thread: Anomaly? or at least a surprise.
  • Next by thread: Re: Anomaly? or at least a surprise.