@ARTICLE{an2019,
     Title={An optimized two-step hybrid block method formulated in variable step-size mode for integrating y''=f(x,y,y') numerically},
     Author={Gurjinder Singh, Higinio Ramos},
     Journal={Numerical Mathematics: Theory, Methods and Applications},
     Volume={12},
     Number={2},
     Pages={640-660},
     Publisher={Global Science Press},
     Year={2019}
}