Re: Re: Re: The graph of (x + 2)^(1/5) + 4 not

*To*: mathgroup at smc.vnet.net*Subject*: [mg103989] Re: [mg103938] Re: [mg103926] Re: The graph of (x + 2)^(1/5) + 4 not*From*: victor chg <kindlychung at gmail.com>*Date*: Wed, 14 Oct 2009 07:58:49 -0400 (EDT)*References*: <868306d90910120643u7f1c2299v2cd1845508dc85b7@mail.gmail.com>

Here is the correct link: http://i35.tinypic.com/11jrtpk.jpg On Wed, Oct 14, 2009 at 11:17 AM, Murray Eisenberg <murray at math.umass.edu>wrote: > Could you please just tell us what you think is wrong with the plot that > Mathematica provides? > > I ask because when I point my browser to the link you provide... > > (1) I get a large number of annoying (and potentially dangerous) > 3rd-party ad-generating items on the URL page that clamor to be allowed > to do their thing. > > (2) The plot finally displayed is of something entirely different -- of > exp(-x^2) and its first two derivatives. > > As to the function (x + 2)^(1/5) + 4 that you asked about: Did you just > try something like the following? > > Plot[(x + 2)^(1/5) + 4, {x,-7,5}] > > If so, then you were probably surprised that the graph ended on the left > at x == -2. And that is precisely what Mathematica should be expected > to do. After all, Mathematica "wants" numbers to be complex when they > can be. And z^(1/5) denotes the PRINCIPAL 5th-root of z, so that when z > is negative, you do NOT get a negative real number, but rather the > non-real, complex principal 5th-root. > > If you want the high school/calculus variety 5th-root function, then you > need to finesse this. For example: > > f[x_] := Sign[x + 2] Abs[x + 2]^(1/5) + 4 > Plot[ f[x], {x,-7,5}] > > (You could use Piecewise instead.) > > victor chg wrote: > > Here is the link to the image: > > http://tinypic.com/view.php?pic=veae6u&s=4 > > > > Victor Chg > > -- > Murray Eisenberg murray at math.umass.edu > Mathematics & Statistics Dept. > Lederle Graduate Research Tower phone 413 549-1020 (H) > University of Massachusetts 413 545-2859 (W) > 710 North Pleasant Street fax 413 545-1801 > Amherst, MA 01003-9305 > > -- -------------------------------------- Neuroscience Research Institute, Peking University, Beijing, P.R.China 100038