Re: Why are the functions different?
- To: mathgroup at smc.vnet.net
- Subject: [mg55652] Re: [mg55609] Why are the functions different?
- From: Sseziwa Mukasa <mukasa at jeol.com>
- Date: Fri, 1 Apr 2005 05:36:28 -0500 (EST)
- References: <200503310624.BAA15126@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On Mar 31, 2005, at 1:24 AM, Helge Stenstroem wrote:
> How are these two functions (f0 and f1) different? f0 can be plotted,
> but f1 cannot.
>
> f1[x_] := Normal[Series[Tanh[x], {x, 0, 5}]]
> f0[x_] := x - x^3/3 + (2*x^5)/15
>
> When evaluated like this:
> f0[x]
> f1[x]
> they look the same.
>
> The following gives error messages if f0 is replaced by f1.
> Plot[{Tanh[z], f0[z]}, {z, -1, 1}]
>
Because x is evaluated before the Series and Normal in f1. Redefine f1
as
f1[y_] := Block[{x}, Normal[Series[Tanh[x], {x, 0, 5}]] /.{x->y}]
and it will work as you expect.
Regards,
Ssezi