Re: Unexpected Output When Plotting...

*To*: mathgroup at smc.vnet.net*Subject*: [mg125499] Re: Unexpected Output When Plotting...*From*: Ray Koopman <koopman at sfu.ca>*Date*: Thu, 15 Mar 2012 00:36:54 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <jjpb6t$p8g$1@smc.vnet.net>

On Mar 13, 10:43 pm, James Kochanski <jwkochan... at mymail.vcu.edu> 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? > > Thanks! > > Jim Kochanski > > Following graphs are plotted from x = -10 to x = 10 > Graph #1 : Plot[Cos[x], {x, -10, 10}] > Graph #2 : Plot[Cos[x + 1], {x, -10, 10}] > Graph #3 : Plot[Cos[x^3], {x, -10, 10}] > Graph #4 : Plot[Cos[x^3 + 1], {x, -10, 10}] > > 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}] The problem is that you're asking for cube roots of negative values, which give complex values where you want negative reals. To get negative reals, define qbrt = Piecewise[{{-(-#)^(1/3),#<0}},#^(1/3)]& , then change #^(1/3) in your code to qbrt[#] .