kdata_xstddev,
kdata_ystddev — compute
population standard deviation of data
#include <cairo.h>
#include <kplot.h>
double
kdata_xstddev(const struct kdata
*data);
double
kdata_ystddev(const struct kdata
*data);
The kdata_xstddev and
kdata_ystddev functions compute the population
standard deviation of the arithmetic mean of data.
If the data source has zero entries,
kdata_xstddev and
kdata_ystddev return 0.0. Otherwise, they returns
the standard deviation value.