Re: Evaluation question

*To*: mathgroup at smc.vnet.net*Subject*: [mg80340] Re: Evaluation question*From*: David Bailey <dave at Remove_Thisdbailey.co.uk>*Date*: Sat, 18 Aug 2007 05:32:44 -0400 (EDT)*References*: <fa13jg$nua$1@smc.vnet.net>

Yaroslav Bulatov wrote: > Abs[-1 - 2 E - E ^2 + (1 + E)^2] > Evaluate[%] > > Why is the "N::meprec" message only printed once? > > Although Mathematica appears to evaluate expressions from scratch, for performance reasons, it keeps information that lets it know that an expression cannot change by further evaluation. This information is quite subtle, because if an expression contains a variable, it recognises that it needs to re-evaluate if the variable is given a value. David Bailey http://www.dbaileyconsultancy.co.uk