Beta inverse cumulative distribution function
X = betainv(P,A,B)
X = betainv(P,A,B) computes the inverse of the beta cdf with parameters specified by A and B for the corresponding probabilities in P. P, A, and B can be vectors, matrices, or multidimensional arrays that are all the same size. A scalar input is expanded to a constant array with the same dimensions as the other inputs. The parameters in A and B must all be positive, and the values in P must lie on the interval [0, 1].
The inverse beta cdf for a given probability p and a given pair of parameters a and b is
and B( · ) is the Beta function. Each element of output X is the value whose cumulative probability under the beta cdf defined by the corresponding parameters in A and B is specified by the corresponding value in P.
p = [0.01 0.5 0.99]; x = betainv(p,10,5) x = 0.3726 0.6742 0.8981
According to this result, for a beta cdf with a = 10 and b = 5, a value less than or equal to 0.3726 occurs with probability 0.01. Similarly, values less than or equal to 0.6742 and 0.8981 occur with respective probabilities 0.5 and 0.99.