RE: Why can't Mathematica do this simple integral ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg36895] RE: Why can't Mathematica do this simple integral ?*From*: Madhusudan Singh <spammers-go-here at yahoo.com>*Date*: Tue, 1 Oct 2002 04:45:26 -0400 (EDT)*References*: <an14h9$ie2$1@smc.vnet.net>*Reply-to*: spammers-go-here at yahoo.com*Sender*: owner-wri-mathgroup at wolfram.com

On Friday 27 September 2002 04:18 am, DrBob, as drbob at bigfoot.com, held forth the following in comp.soft-sys.math.mathematica (<an14h9$ie2$1 at smc.vnet.net>) : > You would need to make assumptions about y, and you can't. The function > and the limits have to take care of that, and when you try to do that, > you end up with an expression that has different antiderivatives on > different regions, for different values of x. So, you have to break it > up. The assumption x > 0 implies that x is real, so Im[x]==0 is > unnecessary. > > one = Integrate[Cosh[2 (y - x)] > 2 y, {y, Min[x, 1/2], 1/2}, Assumptions -> {x > 0}]; > two = Integrate[Cosh[2 (x - y)] 2 > y, {y, 0, Min[x, 1/2]}, Assumptions -> {x > 0}]; > one + two // FullSimplify > Plot[{one, two, one + two}, {x, 0, 1/2}]; > > (1/4)*E^(-1 - 2*x)*(E + (-2 + E)*E^(4*x)) > > Bobby Treat > > -----Original Message----- > From: Madhusudan Singh [mailto:spammers-go-here at yahoo.com] To: mathgroup at smc.vnet.net > Subject: [mg36895] Why can't Mathematica do this simple integral ? > > Hi > I have been trying to integrate the following : > > Integrate[Cosh[2 Abs[x-y]] 2 y, {y,0,1/2}, > Assumptions->{Im[x]==0,x>0}] > > However, Mathematica chokes and simply returns the integral as > it is. However, if I > split up the integral into two portions, it quickly gives me an answer > for the parts. Is > there something implicit that I am missing in the Assumptions ? > > Thanks, > > MS. > Thanks for your response. But why can't Mathematica give the answer in the If[x.....] form ? Anyways, I will try what you suggest. -- Linux 12:53pm up 27 min, 1 user, load average: 0.19, 0.15, 0.09