Since discarded excitations increase autocorrelation of the projected energy, the standard error σ E of a discarding-GAS excitation generator will usually be larger than for the a priori selection provided by the GAS-PCHB scheme. Also the p gen (i, j) for discarding GAS algorithms is generally lower than for corresponding a priori GAS algorithms; this has the effect of leading to a smaller imaginary time-step for the discarding-GAS algorithm.