where @math{x_i} are the elements of the dataset data. The
absolute deviation from the mean provides a more robust measure of the
width of a distribution than the variance. This function computes the
mean of data via a call to gsl_stats_mean
.
This function is useful if you have already computed the mean of data (and want to avoid recomputing it), or wish to calculate the absolute deviation relative to another value (such as zero, or the median).