Deyin Zhao Zhongcheng Wang Yongming Dai Importance of the first-order derivative formula in the Obrechkoff method. 65-75 2005 167 Computer Physics Communications 2 http://dx.doi.org/10.1016/j.cpc.2005.01.009 db/journals/cphysics/cphysics167.html#ZhaoWD05