Linear time isotonic and unimodal regression in the L1 and Linfinity norms

We consider L"1-isotonic regression and L"~ isotonic and unimodal regression. For L"1-isotonic regression, we present a linear time algorithm when the number of outputs are bounded. We extend the algorithm to construct an approximate isotonic regression in linear time when the output range is bounded. We present linear time algorithms for L"~ isotonic and unimodal regression.