Inverse incomplete gamma function
x = gammaincinv(y,a)
x = gammaincinv(y,a,tail)
x = gammaincinv(y,a) evaluates the inverse
incomplete gamma function for corresponding elements of
y = gammainc(x,a). The elements of
be in the closed interval
[0,1], and those of
be real and the same size (or either can be a scalar).
x = gammaincinv(y,a,tail) specifies the
tail of the incomplete gamma function. Choices are
default) to use the integral from 0 to
use the integral from
x to infinity.
These two choices are related as:
gammaincinv(y,a,'upper') = gammaincinv(1-y,a,'lower').
y is close to 0, the
provides a way to compute
x more accurately than
y from 1.
The lower incomplete gamma function is defined as:
gamma(a). The upper incomplete gamma function is defined as:
gammaincinv computes the inverse of the
incomplete gamma function with respect to the integration limit
gammaincinv(y,a) approaches infinity. For small
 Cody, J., An Overview of Software Development for Special Functions, Lecture Notes in Mathematics, 506, Numerical Analysis Dundee, G. A. Watson (ed.), Springer Verlag, Berlin, 1976.
 Abramowitz, M. and I.A. Stegun, Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series #55, Dover Publications, 1965, sec. 6.5.
This function fully supports tall arrays. For more information, see Tall Arrays.
Usage notes and limitations:
Output is always complex.
Strict single-precision calculations are not supported. In the generated code, single-precision inputs produce single-precision outputs. However, variables inside the function might be double-precision.