COMPUTE QUANTILE

        [SIC\]COMPUTE OutVar QUANTILE InVar

    Compute  the  k-quantiles (i.e. the k-1 values which split the data in k
    subsets of equal or almost-equal sizes) of the InVar  array  in  OutVar.
    For  convenience  the  0-th (minimum value) and the k-th (maximum value)
    quantiles of the InVar array are also computed.

    OutVar must be an array of shape [...,k+1]. The leading  dimensions,  if
    any, must match the leading dimensions of the InVar array.

    In practice this means:
    - the median (2-quantile) needs k+1=3 (return min, median, max),
    - the quartiles need k+1=5,
    and so on.