Erfc
Defined in header <cmath>
.
Description
Computes the complementary error function of num
, that is 1.0 - std::erf(num)
, but without loss of precision for large num
.
The library provides overloads of std::erfc
for all cv-unqualified floating-point types as the type of the parameter num
(od C++23).
Additional Overloads are provided for all integer types, which are treated as double.
Declarations
- C++23
- C++11
// 1)
/* floating-point-type */ erfc( /* floating-point-type */ num );
// 2)
float erfcf( float num );
// 3)
long double erfcl( long double num );
// 4)
template< class Integer >
double erfc ( Integer num );
// 1)
float erfc ( float num );
// 2)
double erfc ( double num );
//3)
long double erfc ( long double num );
// 4)
float erfcf( float num );
// 5)
long double erfcl( long double num );
// 6)
template< class Integer >
double erfc ( Integer num );
Parameters
num
- floating-point or integer value
Return value
If no errors occur, value of the complementary error function of num, that is math here
, is returned.
If a range error occurs due to underflow, the correct result (after rounding) is returned.
Error handling
Errors are reported as specified in math_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559):
If the argument is +∞
, +0
is returned
If the argument is -∞
, 2
is returned
If the argument is NaN, NaN is returned
Notes
For the IEEE-compatible type double, underflow is guaranteed if num > 26.55
.
The additional overloads are not required to be provided exactly as Additional Overloads.
They only need to be sufficient to ensure that for their argument num
of integer type,
std::erfc(num)
has the same effect as std::erfc(static_cast<double>(num))
.
Examples
#include <cmath>
#include <iomanip>
#include <iostream>
double normalCDF(double x) // Phi(-∞, x) aka N(x)
{
return std::erfc(-x / std::sqrt(2)) / 2;
}
int main()
{
std::cout
<< "normal cumulative distribution function:\n"
<< std::fixed
<< std::setprecision(2);
for (double n = 0; n < 1; n += 0.1)
std::cout
<< "normalCDF(" << n << ") = "
<< 100 * normalCDF(n) << "%\n";
std::cout
<< "special values:\n"
<< "erfc(-Inf) = "
<< std::erfc(-INFINITY) << '\n'
<< "erfc(Inf) = "
<< std::erfc(INFINITY) << '\n';
}
normal cumulative distribution function:
normalCDF(0.00) = 50.00%
normalCDF(0.10) = 53.98%
normalCDF(0.20) = 57.93%
normalCDF(0.30) = 61.79%
normalCDF(0.40) = 65.54%
normalCDF(0.50) = 69.15%
normalCDF(0.60) = 72.57%
normalCDF(0.70) = 75.80%
normalCDF(0.80) = 78.81%
normalCDF(0.90) = 81.59%
normalCDF(1.00) = 84.13%
special values:
erfc(-Inf) = 2.00
erfc(Inf) = 0.00