  Following similar approaches in the past, the Schrodinger equation for three
neutrino propagation in matter of constant density is solved analytically by
two successive diagonalizations of 2x2 matrices. The final result for the
oscillation probabilities is obtained directly in the conventional parametric
form as in the vacuum but with explicit simple modification of two mixing
angles ($\theta_{12}$ and $\theta_{13}$) and mass eigenvalues.
