## Struct template variance_impl

boost::accumulators::impl::variance_impl — Iterative calculation of variance.

## Synopsis

template<typename Sample, typename MeanFeature, typename Tag>
struct variance_impl : public accumulator_base {
template<typename Args> variance_impl(Args const &);
template<typename Args> void operator()(Args const &);
result_type result(dont_care) const;
};

## Description

Iterative calculation of sample variance according to the formula

where

is the estimate of the sample mean and is the number of samples.

Note that the sample variance is not defined for .

A simplification can be obtained by the approximate recursion

because the difference

converges to zero as . However, for small the difference can be non-negligible.

###
`variance_impl`

public
construct/copy/destruct

template<typename Args> variance_impl(Args const & args);

###
`variance_impl`

public member functions

template<typename Args> void operator()(Args const & args);

result_type result(dont_care) const;