Re: Why are the functions different?

*To*: mathgroup at smc.vnet.net*Subject*: [mg55663] Re: Why are the functions different?*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Fri, 1 Apr 2005 05:37:14 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 3/31/05 at 1:24 AM, helge.stenstrom.NOSPAM at NOSPAMericsson.com (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}] The problem is evaluation with a numeric argument. If you supply f1 with a numeric argument, Tanh evaluates to a number and the arguements to Series will not be valid. This can be fixed by using Set instead of SetDelayed in the definition of f1, i.e., f1[x_] = Normal[Series[Tanh[x], {x, 0, 5}]] With this definition, the rhs gets evaluated to x - x^3/3 +(2*x^5)/15 before any number is supplied to f1 and f1[x] will evaluate to a number when x is a number as Plot requires. -- To reply via email subtract one hundred and four