Simplifying gamma function in equation

1k Views Asked by At

I Know the integral should give me some sort of gamma function, how do I continue to simplify the steps?

1

There are 1 best solutions below

3
On BEST ANSWER

What I could suggest is to expand (y - n tau)^(n-1) using the binomaial expansion. So, omiting coefficients, the summation will reduce to the summation of integrals of things looking as Exp[y(t-lambda)] y^k [k varying between 0 and (n-1)]. The result of this last integral, between zero and infinity is just (lambda - t)^(-k-1) Gamma[1+k]. Then, for a given value of "n", M(t) seems to write as

lambda^n Exp[n tau lambda] / Gamma[n] Sum[ Binomial[n-1,k] (lambda - tau)^(-k-1) Gamma[k+1] (-n tau)^(n-k-1), {k,0,n-1} ]

I checked the above formula for different values of "n" and it seems to be OK. Let me know.

Another way, simpler, will consist in the change of variable y = z + n tau I suggested earlier; it leads to the integration of something looking like Exp[a z] z^n between (-n tau) and infinity