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## Struct template lazy_variance_impl

boost::accumulators::impl::lazy_variance_impl — Lazy calculation of variance.

## Synopsis

    // In header: <boost/accumulators/statistics/variance.hpp>

    template<typename Sample, typename MeanFeature>
    struct lazy_variance_impl {
      // types
      typedef numeric::functional::average< Sample, std::size_t >::result_type result_type;

      // construct/copy/destruct
      lazy_variance_impl(dont_care);

      // public member functions
      template<typename Args> result_type result(Args const &) const;
    };

## Description

Default sample variance implementation based on the second moment moment<2>, mean and count.

Equation 1.21.

where

Equation 1.22.

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

### `lazy_variance_impl` public construct/copy/destruct

1.     lazy_variance_impl(dont_care);

### `lazy_variance_impl` public member functions

1.     template<typename Args> result_type result(Args const & args) const;