Confusing results with N[expr]?

*To*: mathgroup at smc.vnet.net*Subject*: [mg62318] Confusing results with N[expr]?*From*: "Thomas Bohl" <Thomas.Bohl at cern.ch>*Date*: Sat, 19 Nov 2005 23:19:01 -0500 (EST)*Organization*: CERN*Sender*: owner-wri-mathgroup at wolfram.com

I have the impression that since some time (since Vers. 5.0?) N[expr] does not give anymore the results I expect. The following code should illustrate this: N[a] = 2.; k = z*(a*Pi); N[k] > 6.28319 z (* "a" and "Pi" are replaced by their numerical value as > expected *) k = z^(a*Pi) N[k] > z^(3.14159 a) (* "Pi" is replaced by its numerical value but not "a", > why not? *) There are more examples of this behaviour: If the expression is Log[z*a*Pi], the numerical values of "a" and "Pi" are evaluated, if the expression is Exp[z*a*Pi] the numerical value of "a" is not evaluated. Why not? The motivation behind my question is that I was used to write expressions symbolically and assign numerical values with N[expr] = num. value. This way you could keep those expressions symbolically and just apply //N when you needed numerical values. Now it seems that I have lost this possibility. Could you please comment my observation and maybe suggest a way out? Thank you very much for any idea. Kind regards, Thomas.

**Follow-Ups**:**Re: Confusing results with N[expr]?***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>