Calculates values for a gamma distribution.
GAMMADIST(x, α, β, mode)
The gamma distribution is a family of continuous probability distributions, with parameters α (shape) and β (scale).
If mode is 0, GAMMADIST calculates the probability density function of the gamma distribution:
If mode is 1, GAMMADIST calculates the cumulative distribution function of the gamma distribution:
x must be greater than or equal to 0.
GAMMADIST(2, 1, 1, 1)
returns approximately 0.86.