常用的统计数学函数：sum, sd, mean, cv

/***********************************************************************
 * @file math.h
 * @ingroup math
 * @author wangqing
 * @date 2020-05-14
 * @brief 常用统计计算
 ***********************************************************************/

#ifndef __MATH_H__
#define __MATH_H__

#include <cmath>
#include <iterator>
#include <numeric>

namespace math {
using namespace std;
template <class _InIt, class _Ty>
inline _Ty sum(const _InIt _First, const _InIt _Last, _Ty _Val) {
    _Adl_verify_range(_First, _Last);
    return _Val = accumulate(_First, _Last, _Val);
}

template <class _InIt, class _Ty>
inline _Ty mean(const _InIt _First, const _InIt _Last, _Ty _Val) {
    _Adl_verify_range(_First, _Last);
    return _Val = accumulate(_First, _Last, _Val) / distance(_First, _Last);
}

template <class _InIt, class _Ty>
inline _Ty sd(const _InIt _First, const _InIt _Last, _Ty _Val) {
    _Adl_verify_range(_First, _Last);
    auto   m = mean(_First, _Last, _Val);
    double accum{};
    for_each(
        _First, _Last, [&](decltype(*_First) d) { accum += pow((d - m), 2); });
    return _Val = sqrt(accum / distance(_First, _Last));
    return _Val;
}

template <class _InIt, class _Ty>
inline _Ty cv(const _InIt _First, const _InIt _Last, _Ty _Val) {
    _Adl_verify_range(_First, _Last);
    auto m      = mean(_First, _Last, _Val);
    auto s      = sd(_First, _Last, _Val);
    return _Val = s / m * 100;
}
}  // namespace math
#endif  // __MATH_H__

#endif // __MATH_H__