# DirectionalStatisticsAccumulator class

`DirectionalStatisticsAccumulator`

computes directional mean and standard deviation by accumulating
a unit vector with the input value as angle.

Samples are added one by one, using the `Push`

method. Other members are used to retrieve estimates of
the sample statistics based on the samples seen up to that point.

It is possible to accumulate samples in different objects (e.g. when processing with multiple threads),
and add the accumulators together using the `+`

operator.

## Functions

- void Reset()
- Reset the accumulator, leaving it as if newly allocated.
- void Push(dip::dfloat x)
- Add a sample to the accumulator
- auto Number() const -> dip::uint
- Number of samples
- auto Mean() const -> dip::dfloat
- Unbiased estimator of population mean
- auto Variance() const -> dip::dfloat
- Unbiased estimator of population variance
- auto StandardDeviation() const -> dip::dfloat
- Estimator of population standard deviation (it is not possible to derive an unbiased estimator)

## Operators

- auto operator+=(dip::DirectionalStatisticsAccumulator const& b) -> dip::DirectionalStatisticsAccumulator&
- Combine two accumulators