*(English)*Zbl 1046.34036

Here, second-order forward dynamic equations

and their companion backward problems

under the boundary condition $u\left(a\right)=u\left(b\right)=0$ are studied. The equations are defined on compact time scales (i.e., compact subset of the reals) with a certain symmetry property, ${u}^{{\Delta}}$ resp. ${u}^{\nabla}$ denote ${\Delta}$- resp. $\nabla $-derivative of $u$, and $\sigma ,\rho $ are the jump operators.

The primary purpose of the authors is to study the upper and lower solutions of such nonlinear companion dynamic equations that produce crossed symmetric solutions on time scales. Upper and lower solutions for complementary pairs of forward and backward dynamic boundary value problems are introduced, a quasilinearization procedure for approximating the companion dynamic problems associated with the ${\Delta}$- and $\nabla $-derivatives is established and qualitative results are given. Finally, several numerical experiments close their discussion.

##### MSC:

34B15 | Nonlinear boundary value problems for ODE |

39A10 | Additive difference equations |

65M06 | Finite difference methods (IVP of PDE) |

34B10 | Nonlocal and multipoint boundary value problems for ODE |