eta =	{0.10, 0.15, 0.20, 0.25, 0.30, 0.50, 0.60, 0.70, 0.90}
maximum depth =	{6, 8, 10, 12, 15, 20, 30}
minimum child weight=	{1, 3, 5, 7, 9}
gamma =	{0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9}
subsample =	{0.1, 0.3, 0.5, 0.7, 0.9}
sampling method =	{uniform, gradient based}