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## Struct template lazy_weighted_variance_impl

boost::accumulators::impl::lazy_weighted_variance_impl — Lazy calculation of variance of weighted samples.

## Synopsis

    template<typename Sample, typename Weight, typename MeanFeature>
    struct lazy_weighted_variance_impl {
      // types
      typedef numeric::functional::multiplies< Sample, Weight >::result_type       weighted_sample;
      typedef numeric::functional::average< weighted_sample, Weight >::result_type result_type;

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

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

## Description

The default implementation of the variance of weighted samples is based on the second moment (weighted_moment<2>) and the mean (weighted_mean):

Equation 1.42.

where is the number of samples.

### `lazy_weighted_variance_impl` public construct/copy/destruct

1.     lazy_weighted_variance_impl(dont_care);

### `lazy_weighted_variance_impl` public member functions

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