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: [mg90297] Re: [mg90250] Anomaly? or at least a surprise.
  • From: Bob Hanlon <hanlonr at cox.net>
  • Date: Fri, 4 Jul 2008 04:02:01 -0400 (EDT)
  • Reply-to: hanlonr at cox.net

Plot[D[ArcTan[x]], {x, -10, 10}, PlotRange -> Full] gives the Plot of ArcTan[x], i.e., without the variable the D had no effect. The Plot you wanted would be

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


Bob Hanlon

---- Steve Gray <stevebg at roadrunner.com> 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




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