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How to deal with this integral

• To: mathgroup at smc.vnet.net
• Subject: [mg97783] How to deal with this integral
• From: paperkite rainyday <paperkite at gmail.com>
• Date: Sat, 21 Mar 2009 05:19:41 -0500 (EST)

hi everybody,

I want to deal with this integral with Mathematica:

Integrate[a*b*Exp[-(a+b)]*DiracDelta[1/(4*a)+1/(4*b)+c-t],{a,0,Infinity},{b,0,Infinity},{c,0,Infinity},Assumptions->t>0],

Mathematica 6.0 gives 0. But it is wrong, the correct result is
(1/2)*x^2*Exp[-x]*((1+x)*BesselK[0,x]+(2+x+2/x)*BesselK[1,x]),
where x=1/(2*t).

What's wrong?

Thanks,


paperkite