José A. Reyes Fernando García-Alonso José M. Ferrándiz Jesús Vigo-Aguiar Numeric multistep variable methods for perturbed linear system integration. 63-79 2007 190 Applied Mathematics and Computation 1 http://dx.doi.org/10.1016/j.amc.2007.01.017 db/journals/amc/amc190.html#ReyesGFV07