The problem of two-point ray tracing in a perturbed anisotropic inhomogeneous medium is discussed. It is assumed that the ray Omega in the perturbed medium is situated close to the ray Omega0, constructed in the background medium. Simple expressions for the initial-value slowness vector of the perturbed ray are found. These expressions are explicit; their application does not require a solution of any system of equations. The solution needs only the 6x6 ray propagator matrix in Cartesian coordinates to be known, determined along the ray Omega0 in the background medium. The results remain valid even for paraxial ray approximations (in which the perturbed and background media coincide, but the ray Omega is different from the ray Omega0).
Anisotropic inhomogeneous media, ray perturbation methods, two-point ray tracing.
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