Help -- Weird integration behavior

*To*: mathgroup at smc.vnet.net*Subject*: [mg49345] Help -- Weird integration behavior*From*: miked378 at hotmail.com (Mike)*Date*: Thu, 15 Jul 2004 07:00:08 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

I'm working on a project that I last worked on a couple of years ago, and I'm trying to pick up where I left off. I had been doing some integrations using Mathematica 4.2, and all was well. I'm now trying to use the same workbook, but with Mathematica 5.0, and the integration that previously seemed to work now gives me a value of zero. Interestingly, when I run the same file on different versions of Mathematica, I get either zero or an expression: --v5.0 (student), Macintosh: zero --v5.0, Solaris: zero --v4.2, Macintosh: expression --v4.0, Windows: expression Here's the code: F[x_, t_] = (ks (UnitStep[x] - UnitStep[x - 0.5]))(UnitStep[t] - UnitStep[t - 0.5]); phi[n_, x_] = Sqrt[2] Sin[n Pi x/L] G[n_, t_] = Integrate[F[x, t] phi[n, x], {x, 0, L}] It's the output of this last line that's interesting to me -- either an expression (I hope) or zero. My questions are: -- Did something change in 5.0 that makes it so that this integration doesn't work correctly? -- Can anybody out there reproduce my problem (i.e., run these three cells on different versions and produce different answers?) Thanks for the help!

**Follow-Ups**:**Re: Help -- Weird integration behavior***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>