Re: how to explain this weird effect? Integrate

*To*: mathgroup at smc.vnet.net*Subject*: [mg46261] Re: how to explain this weird effect? Integrate*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Thu, 12 Feb 2004 22:46:24 -0500 (EST)*Organization*: Universitaet Leipzig*References*: <c0ftbt$c7p$1@smc.vnet.net>*Reply-to*: kuska at informatik.uni-leipzig.de*Sender*: owner-wri-mathgroup at wolfram.com

Hi, Limit[Limit[r, n -> m], m -> 2] Regards Jens steve_H wrote: > > I type: > > r = Integrate[Sin[m x] Sin[n x], {x, 0, 2 Pi}] > > then I type > > r /. {n -> 2, m -> 2} > > I get error (1/0 expression encountered) and no result. > > but when I let m=2 and n=2 right into the integral first, it works: > > r = Integrate[Sin[2 x] Sin[2 x], {x, 0, 2 Pi}] > > and I get Pi as expected. > > I wanted to integrate this once, and try the output for different n,m. > > I did not think it will make a difference as to when I replace m and n > by their numerical values, but Mathematica disagrees. > > I know Mathematica is correct in this, since it is clear from the result > of the integration why I get 1/0. But it seems to me I should > get the same result if I replace m,n inside the integral before > the integration operation starts, or replace them afterwords. > > For example, when I type > > Integrate[Sin[m x], {x, 0, Pi}] > % /. m -> 4 > > I get zero. > > and when I replace m with 4 inside the integral first, I get the same > result as above: > > Integrate[Sin[4 x], {x, 0, Pi}] > 0 > > So, what do you think? is there something I am missing here? > > thanks > Steve