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MathGroup Archive 2012

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Re: Unexpected Output When Plotting...

  • To: mathgroup at smc.vnet.net
  • Subject: [mg125495] Re: Unexpected Output When Plotting...
  • From: Bill Rowe <readnews at sbcglobal.net>
  • Date: Thu, 15 Mar 2012 00:35:30 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com

On 3/14/12 at 12:40 AM, jwkochanski at mymail.vcu.edu (James Kochanski)
wrote:

>Can anyone explain to me why Graphs #5 and #6 (please see below) do
>not include any output for x < 0 and x < -1, respectively?

>Following graph is only plotted from x = 0 to x = 10 Graph #5
>:   Plot[Cos[(x^3)^(1/3)], {x, -10, 10}]

>Following graph is only plotted from x = -1 to x = 10 Graph #6
>:   Plot[Cos[(x^3 + 1)^(1/3)], {x, -10, 10}]

By default, Mathematica assumes all variables are complex
variables. When taking a cube root of a negative value,
Mathematica does not by default return real values. Instead,
Mathematica returns a complex value by default. And since Plot
cannot plot a complex value, nothing is plotted in the regions
you note above.




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