Re: A Problem with Simplify

*To*: mathgroup at smc.vnet.net*Subject*: [mg87675] Re: A Problem with Simplify*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Tue, 15 Apr 2008 05:53:54 -0400 (EDT)

On 4/14/08 at 5:43 AM, popkov at gmail.com (Alexey Popkov) wrote: >Try the following: >Integrate[Exp[(a - 1)*x], x] /. a -> 1 >Integrate[Cos[(a - 1)*x], x] /. a -> 1 >Integrate[(a - 1)^x, {x, -1, 0}] /. a -> 1 >Integrate[Cos[a x]/Sin[x], x] /. a -> 1 >There is the ONE underlying BUG! There is no bug here. Each of the integrals you do above result in an expression divided by (a-1). The replacement rule simply substitutes 1 for a everywhere. Consequently, the denominator of each integral evaluates to 0 and Mathematica returns either Indeterminate or ComplexInfinity as it should. Where you expecting a to be replaced by 1 before the integration was done? If so, the syntax should be written Integrate[f/.a->1,x] Or perhaps you were expecting Mathematica to simplify the results of the integral before replacing a with 1. If so, you need either FullSimplify[Integrate[f,x]]/.a->1 or Simplify[Integrate[f,x]]/.a->1 However, neither of these are guaranteed to remove the singularity. So, these may result in exactly what you got.