Deviation of the waves in an inhomogeneous medium

Using the formula found by Noorbala and Sepehrinia, the wave deviation in an inhomogeneous medium with continuous variation of propagation velocity is deduced. For electromagnetic waves (light) that propagate in the gravitational field, the deduced deviation is identical to that calculated from General Relativity. The method and its consequences are a good example that verifies the Noorbala-Sepehrinia's formula as well as the mecano-optics analogy (Hamilton's principle / principle of stationary action and Fermat's principle) for the bodies movement in the gravitational field.