# DESCRIPTION

The

**kdata_stddev_alloc** creates a reference-counted data sources for

kplot(3). It attaches to zero or more existing data sources and, when they update their values, tracks the standard deviation (via the unbiased sample variance) of sequence of updated values.

It attaches to zero or more existing data sources and, when they update their values per-index, tracks the standard deviation (via the unbiased sample variance) of the sequence of updated values. Thus, if a standard deviation data source is attached to two sources, its y-value for pair zero will reflect the standard deviation from the mean of all values set to pair zero's y-value in the sources. Note that the indexing is absolute: if attached to a bucket or histogram, pair index zero refers to the first internal data storage, not storage mapped from the bucket or histogram.

If

*source* is not

NULL, the internal buffer is initialised to the size of the source and all of its x values. The standard deviation is initialised to zero with zero updates. Otherwise, the internal buffer is sized to zero.

Further data sources may be attached with

kdata_stddev_attach(3).