Re: Not all points plot on my graph...

*To*: mathgroup at smc.vnet.net*Subject*: [mg105244] Re: Not all points plot on my graph...*From*: dh <dh at metrohm.com>*Date*: Wed, 25 Nov 2009 02:34:21 -0500 (EST)*References*: <hedte4$lsn$1@smc.vnet.net>

davef wrote: > Why is it when I write this... > > Clear[f, x] > f[x_] = (x + 2)^(2/3) > Plot[f[x], {x, -3, 0}, PlotRange -> {{-3, 0}, {-4, 4}}] > f[-3] > > .. I get no values show in the graph for x<-2 even though f[-3] > evaluates to (-1)^(2/3). > > (-1)^(2/3) evaluates as f[-3]=1 so why wouldn't the point (-3,1) plot > on my graph? > > Hi Dave, your function is multivalued. The principal value is complex for arguments below -2. Mathematica returns the principal value for numeric functions. Read on the internet how the principal value is defined. Where did you see that (-1)^(2/3) evaluates to 1?? This is not the principal value. Daniel