|AHELP for CIAO 4.9 Sherpa v1||
Calculate the complement of the regularized incomplete Gamma function (upper)
Calculate the CEPHES function, igamc, in the range [a > 0; x > 0].
The function, igamc, is defined by
igamc(a,x) = 1 - igam(a,x) = 1/gamma(a) Int_(x)^(Inf) e^(-t) t^(a-1) dt
where "igam" represents the regularized incomplete Gamma function (see "ahelp igam"), and "gamma(a)" the complete Gamma function. (If the igam and igamc functions are *not* regularized, then their sum is not one, but is the complete Gamma function, gamma(a).)
In this implementation, both arguments must be positive. The integral is evaluated by either a power series or continued fraction expansion, depending on the relative values of a and x. Arguments can be in scalar or array form.
Tested at random a, x.
a x Relative error:
Cephes Math Library Release 2.0: April, 1987. Copyright 1985, 1987 by Stephen L. Moshier. Direct inquiries to 30 Frost Street, Cambridge, MA 02140.
Calculate igamc with a=1, x=2.
Calculate igamc with a=[1,2], x=[2,3] .
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