The formulas for the second (two-point) compound derivative of the tra
vel-time curve t ''(x1x2) have been obtained for two-dimensional media
with smooth interfaces of layers with constant velocity gradients. A
calculation scheme is proposed For the three dimensional case. Analysi
s of the calculation complexity has been carried out, and two ways of
solving a two-point boundary problem of ray tracing are compared: adju
stment and variational methods, which both use the Newton method of de
termination of nonlinear-equation roots and of function minimization.
It is shown that the adjustment method gives much more information and
is more efficient as compared with the variational method.