Gamma functionとは 意味・読み方・使い方

語源

The function itself was initially defined as an integral (in modern representation, ${\displaystyle \textstyle \Gamma (x)=\int _{0}^{\infty }e^{-t}t^{x-1}dt}$) for positive real x by Swiss mathematician Leonhard Euler in 1730. The name derives from the notation, Γ(x), which was introduced by Adrien-Marie Legendre (1752—1833) (he referred to it, however, as the Eulerian integral of the second kind). Both Euler's integral and Legendre's notation shift the argument with respect to the factorial, so that for integer n>0, Γ(n) = (n−1)!. Carl Friedrich Gauss preferred π(x), with no shift, but Legendre's notation prevailed. Generalisation to non-integer negative and to complex numbers was achieved by analytic continuation.