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