  Rank two parametric perturbations of operators and matrices are studied in
various settings. In the finite dimensional case the formula for a
characteristic polynomial is derived and the large parameter asymptotics of the
spectrum is computed. The large parameter asymptotics of a rank one
perturbation of singular values and condition number are discussed as well. In
the operator case the formula for a rank two transformation of the spectral
measure is derived and it appears to be the t-transformation of a probability
measure, studied previously in the free probability context. New transformation
of measures is studied and several examples are presented.
