Ensure monotonicity: q10 ≤ q20 ≤ … ≤ q90.
Lowers quantiles below the decode median are corrected rightward: if q[i] > q[i+1], set q[i] = q[i+1]. Upper quantiles above the median are corrected leftward: if q[i] < q[i-1], set q[i] = q[i-1]. Median and mean (index 0) are not modified.
Ensure monotonicity: q10 ≤ q20 ≤ … ≤ q90.
Lowers quantiles below the decode median are corrected rightward: if q[i] > q[i+1], set q[i] = q[i+1]. Upper quantiles above the median are corrected leftward: if q[i] < q[i-1], set q[i] = q[i-1]. Median and mean (index 0) are not modified.