Was trying to fit isotonic regression with non-trivial y_min and y_max: In [*17*]: X Out[*17*]: array([ 1.26336413, 1.31853693, -0.57200917, 0.3072928 , -0.70686507, -0.17614937, -1.59943059, 1.05908504, 1.3958263 , 1.90580318, 0.20992272, 0.02836316, -0.08092235, 0.44438247, 0.01791253, -0.3771914 , -0.89577538, -0.37726249, -1.32687569, 0.18013201]) In [*18*]: iso.isotonic_regression(X, y_min=0, y_max=0.1) Out[*18*]: array([-0.00826919, -0.00826919, -0.00826919, -0.00826919, -0.00826919, -0.00826919, -0.00826919, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344, 0.10449344]) The solution does not satisfy the bounds that each entry should be in [0,0.1] -- Jonathan Taylor Dept. of Statistics Sequoia Hall, 137 390 Serra Mall Stanford, CA 94305 Tel: 650.723.9230 Fax: 650.725.8977 Web: http://www-stat.stanford.edu/~jtaylo