ConstantRate fun ConstantRate(eta: Double = 0.001): ScalarExpr(source)Constant rate eta. ExponentialDecay fun ExponentialDecay(eta: Double = 0.01, k: Double = 1.0E-5): ScalarExpr(source)eta * exp(-k * step). StepDecay fun StepDecay(eta: Double = 0.01, k: Double = 0.001): ScalarExpr(source)eta / (1 + k * step).