Re: A Problem with Simplify
- To: mathgroup at smc.vnet.net
- Subject: [mg87687] Re: A Problem with Simplify
- From: Alexey Popkov <popkov at gmail.com>
- Date: Tue, 15 Apr 2008 06:49:35 -0400 (EDT)
- References: <fu1u56$onj$1@smc.vnet.net>
On 15 =C1=D0=D2, 13:56, Bill Rowe <readn... at sbcglobal.net> wrote: > On 4/14/08 at 5:43 AM, pop... 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. I am expecting to get all partial answers or at least an answer with conditions! On 11 =C1=D0=D2, 09:42, dh <d... at metrohm.ch> wrote: >In the manual one finds: > "For indefinite integrals, Integrate tries to find results that are > correct for almost all values of parameters." This note is located under "MORE INFORMATION" field in the reference for Integrate. And this seems to be false... :( And for definite integrals there is an option "GenerateConditions" that does not work in the most cases (try it with example above: int1 = Integrate[Sin[a*x/L]*Sin[x/L], {x, 0, L}, GenerateConditions -> True] int1 /. a -> 1 The answer is Indeterminate that is false! :( ).