ScalingStacks

Proof. [056V]

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Proof.

Given p,q>0p,q>0, let B⁡(p,q)B(p,q) be the beta function which is defined by

(A.18) B⁡(p,q)≡∫01tp−1​(1−t)q−1​𝑑t.B(p,q)\equiv\int_{0}^{1}t^{p-1}(1-t)^{q-1}dt.

Then the beta function satisfies B⁡(p,q)=Γ⁡(p)​Γ​(q)Γ⁡(p+q)B(p,q)=\frac{\Gamma(p)\Gamma(q)}{\Gamma(p+q)}. The above formulae imply that

(A.19) (β)k(α)k\displaystyle\frac{(\fb)_{k}}{(\fa)_{k}} =\displaystyle= Γ⁡(β+k)Γ⁡(β)⋅Γ⁡(α)Γ⁡(α+k)\displaystyle\frac{\Gamma(\fb+k)}{\Gamma(\fb)}\cdot\frac{\Gamma(\fa)}{\Gamma(\fa+k)}
=\displaystyle= Γ⁡(α)Γ⁡(β)⋅B⁡(β+k,α−β)Γ⁡(α−β)\displaystyle\frac{\Gamma(\fa)}{\Gamma(\fb)}\cdot\frac{B(\fb+k,\fa-\fb)}{\Gamma(\fa-\fb)}
=\displaystyle= Γ⁡(α)Γ⁡(β)​Γ​(α−β)​∫01tβ+k−1​(1−t)α−β−1​𝑑t.\displaystyle\frac{\Gamma(\fa)}{\Gamma(\fb)\Gamma(\fa-\fb)}\int_{0}^{1}t^{\fb+k-1}(1-t)^{\fa-\fb-1}dt.

Now we return to the definition of Φ♯\Ku, combining the above summation,

(A.20) Φ♯⁡(β,α,y)\displaystyle\Ku(\beta,\alpha,y) =\displaystyle= ∑k=0∞(β)k(α)k⋅ykk!\displaystyle\sum\limits_{k=0}^{\infty}\frac{(\beta)_{k}}{(\alpha)_{k}}\cdot\frac{y^{k}}{k!}
=\displaystyle= Γ⁡(α)Γ⁡(β)​Γ​(α−β)​∫01tβ−1​(1−t)α−β−1​∑k=0∞(y​t)k−1k!​𝑑t\displaystyle\frac{\Gamma(\fa)}{\Gamma(\fb)\Gamma(\fa-\fb)}\int_{0}^{1}t^{\beta-1}(1-t)^{\fa-\fb-1}\sum\limits_{k=0}^{\infty}\frac{(yt)^{k-1}}{k!}dt
=\displaystyle= Γ⁡(α)Γ⁡(β)​Γ​(α−β)​∫01ey​t​tβ−1​(1−t)α−β−1​𝑑t.\displaystyle\frac{\Gamma(\fa)}{\Gamma(\fb)\Gamma(\fa-\fb)}\int_{0}^{1}e^{yt}t^{\beta-1}(1-t)^{\fa-\fb-1}dt.

The proof is done.

∎

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