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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
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