Re: Why are the functions different?

*To*: mathgroup at smc.vnet.net*Subject*: [mg55650] Re: [mg55609] Why are the functions different?*From*: "David Park" <djmp at earthlink.net>*Date*: Fri, 1 Apr 2005 05:36:24 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

Helge, Use... f1[x_] = Normal[Series[Tanh[x], {x, 0, 5}]] f0[x_] := x - x^3/3 + (2*x^5)/15 and then everything plots properly. Plot[f0[x], {x, -2, 2}]; Plot[f1[x], {x, -2, 2}]; By using Set instead of DelayedSet on f1, f1 is actually defined as the series approximation. By using DelayedSet and then putting it in Plot, without using Evaluation, Plot substitutes explicit x values into the Series expression, which then makes no sense. For example the 'iterator' portion then takes forms like {1.2, 0, 5} instead of {x, 0, 5} when Plot is trying to evaluate at x = 1.2. Now I wonder if you email address will work after I edit it. David Park djmp at earthlink.net http://home.earthlink.net/~djmp/ From: Helge Stenstroem To: mathgroup at smc.vnet.net [mailto:helge.stenstrom.NOSPAM at NOSPAMericsson.com] 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}] (Mathematica 4.1 on Windows 2000) -- Helge Stenström