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## Function template sum

boost::histogram::algorithm::sum — Compute the sum over all histogram cells (underflow/overflow included by default).

## Synopsis

    // In header: <boost/histogram/algorithm/sum.hpp>

    template<typename A, typename S>
      auto sum(const histogram< A, S > & hist, const coverage cov = coverage::all);

## Description

The implementation favors accuracy and protection against overflow over speed. If the value type of the histogram is an integral or floating point type, accumulators::sum<double> is used to compute the sum, else the original value type is used. Compilation fails, if the value type does not support operator+=. The return type is double if the value type of the histogram is integral or floating point, and the original value type otherwise.

If you need a different trade-off, you can write your own loop or use `std::accumulate`:

    // iterate over all bins
    auto sum_all = std::accumulate(hist.begin(), hist.end(), 0.0);

    // skip underflow/overflow bins
    double sum = 0;
    for (auto&& x : indexed(hist))
      sum += *x; // dereference accessor

    // or:
    // auto ind = boost::histogram::indexed(hist);
    // auto sum = std::accumulate(ind.begin(), ind.end(), 0.0);

Parameters: |
`hist` | Const reference to the histogram.
`cov` | Iterate over all or only inner bins (optional, default: all).
Returns: | accumulator type or double