Function: erfc
Section: transcendental
C-Name: gerfc
Prototype: Gp
Help: erfc(x): complementary error function.
Doc: complementary error function, analytic continuation of
 $(2/\sqrt\pi)\int_{x}^{\infty} e^{-t^{2}}\,dt
 = \text{sign(x)}\kbd{incgam}(1/2,x^{2})/\sqrt\pi$ for real $x \neq 0$.
 The latter expression extends the function definition from real $x$ to
 complex $x$ with positive real part (or zero real part and positive
 imaginary part). This is extended to the whole complex plane by
 the functional equation $\kbd{erfc}(-x) = 2 - \kbd{erfc}(x)$.
 \bprog
 ? erfc(0)
 %1 = 1.0000000000000000000000000000000000000
 ? erfc(1)
 %2 = 0.15729920705028513065877936491739074071
 ? erfc(1+I)
 %3 = -0.31615128169794764488027108024367036903
      - 0.19045346923783468628410886196916244244*I
 @eprog
