gamma function with two parameters

GAMMAINC Regularized incomplete gamma function. Y = GAMMAINC(X,A) evaluates the regularized incomplete gamma function for corresponding elements of X and A. The elements of A must be nonnegative. X and A must be real and the same size (or either can be a scalar). The regularized incomplete gamma function is defined as: gammainc(x,a) = 1 ./ gamma(a) .* integral from 0 to x of t^(a-1) exp(-t) dt For any a>=0, as x approaches infinity, gammainc(x,a) approaches 1. For small x and a, gammainc(x,a) ~ x^a, so gammainc(0,0) = 1. Y = GAMMAINC(X,A,TAIL) specifies the tail of the regularized incomplete gamma function when X is non-negative. Choices are 'lower' (the default) to compute the integral from 0 to X, or 'upper' to compute the integral from X to infinity. These two choices are related as GAMMAINC(X,A,'upper') = 1 - GAMMAINC(X,A,'lower'). When the upper tail value is close to 0, the 'upper' option provides a way to compute that value more accurately than by subtracting the lower tail value from 1. Warning: When X is negative, Y can be inaccurate for abs(X) > A+1. Y = GAMMAINC(X,A,'scaledlower') and GAMMAINC(X,A,'scaledupper') return the regularized incomplete gamma function, scaled by GAMMA(A+1)*EXP(X)/X^A. These functions are unbounded above, but are useful for values of X and A where GAMMAINC(X,A,'lower') or GAMMAINC(X,A,'upper') underflow to zero. See also GAMMAINCINV, GAMMA, GAMMALN, PSI. Documentation for gammainc doc gammainc Other uses of gammainc codistributed/gammainc gpuArray/gammainc tall/gammainc