Re: Simple integration that Mathematica can't do?
- To: mathgroup at smc.vnet.net
- Subject: [mg27809] Re: Simple integration that Mathematica can't do?
- From: "Tom Hardy" <tomhardy at erols.com>
- Date: Sat, 17 Mar 2001 05:41:39 -0500 (EST)
- References: <98a200$cr8@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Try the replacement x=>x+1 and change the integration limits to 0 to big. I get (1+a)E^-a with 3.0. Agree, Mathematica could be better. BTW is the new version any better with regard to graphics? I never could get them to print correctly under 3.0. "A. E. Siegman" <siegman at stanford.edu> wrote in message news:98a200$cr8 at smc.vnet.net... > I'm a little surprised that Mathematica can't do the following fairly > simple calculation: > > f[x_] := Sqrt[4a^3] x Exp[-a x] > > u = Integrate[ f[x] f[x - 1], {x, 1, Infinity}, > Assumptions -> {Re[a] > 0}] > > even though if I break it apart by hand into the form > > u1 = 4a^3 Exp[a] Integrate[x^2 Exp[-2a x], {x, 1, Infinity}, > Assumptions -> {Re[a] > 0}] > > u2 = 4a^3 Exp[a] Integrate[x Exp[-2a x], {x, 1, Infinity}, > Assumptions -> {Re[a] > 0}] > > u = u1 - u2 > > it can do both of the component integrals with no problem. >