Additional Notes, taken from source.
WHICH --> Integer indicating which of the next four argument
values is to be calculated from the others.
Legal range: 1..4
iwhich = 1 : Calculate P and Q from X,Y,A and B
iwhich = 2 : Calculate X and Y from P,Q,A and B
iwhich = 3 : Calculate A from P,Q,X,Y and B
iwhich = 4 : Calculate B from P,Q,X,Y and A
P <--> The integral from 0 to X of the chi-square
distribution.
Input range: [0, 1].
Q <--> 1-P.
Input range: [0, 1].
P + Q = 1.0.
X <--> Upper limit of integration of beta density.
Input range: [0,1].
Search range: [0,1]
Y <--> 1-X.
Input range: [0,1].
Search range: [0,1]
X + Y = 1.0.
A <--> The first parameter of the beta density.
Input range: (0, +infinity).
Search range: [1D-100,1D100]
B <--> The second parameter of the beta density.
Input range: (0, +infinity).
Search range: [1D-100,1D100]
