Wednesday, 8 May 2019

integration - Solving the Definite Integral intinfty0frac1tfrac32efracat,mathrmerf(sqrtt),mathrmdt



I would like to solve the following integral




01t32eaterf(t)dt



with Re(a)>0 and erf the error function.
Is it possible to given an closed form solution for this integral? Thank you.



Edit: Maybe this helps
L(erf(t),s)=1s1+s
L1(t32eat)=1πasin(2as)




with L the Laplace transform.



Therefore it should be
01t32eaterf(t)dt=01s1+sπasin(2as)ds


Answer



Represent the erf as an integral and work a substitution. To wit, the integral is



2π10dv0dtte(a/t+v2t)



To evaluate the inner integral, we sub y=a/t+v2t. Then the reader can show that




0dtte(a/t+v2t)=22vadyy24av2ey



The latter integral is easily evaluated using the sub y=2vacoshw and is equal to



22vadyy24av2ey=20dwe2vacoshw=2K0(2va)



where K0 is the modified Bessel function of the second kind of zeroth order. Now we integrate this expression with respect to v and multiply by the factors outside the integral to get the final result:





0dtt3/2ea/terf(t)=4π10dvK0(2va)=2π[K0(2a)L1(2a)+K1(2a)L0(2a)]




where L is a Struve function.


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