#include <math.h> double erf(double x); float erff(float x); double erfc(double x); float erfcf(float x);
erf calculates an approximation to the "error function",
which estimates the probability that an observation will fall within
x standard deviations of the mean (assuming a normal
erfc calculates the complementary probability; that is,
1 - erf(x).
erfc is computed directly,
so that you can use it to avoid the loss of precision that would
result from subtracting large probabilities (on large x) from 1.
erfcf differ from
erfc only in the
argument and result types.
For positive arguments,
erf and all its variants return a
probability--a number between 0 and 1.
None of the variants of
erf are ANSI C.
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