where formula_21 is a reconstruction offset value in the range of 0 to 1 as a fraction of the step size. Ordinarily, formula_22 when quantizing input data with a typical probability density function (pdf) that is symmetric around zero and reaches its peak value at zero (such as a Gaussian, Laplacian, or generalized Gaussian pdf). Although formula_21 may depend on formula_10 in general, and can be chosen to fulfill the optimality condition described below, it is often simply set to a constant, such as formula_25. (Note that in this definition, formula_26 due to the definition of the function, so formula_27 has no effect.)