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.
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