where \mathbf{R}_v is the visibilities covariance matrix (sources), \sigma_s^2 is the power of the interferer, and \sigma_n^2 is the noise power, and \dagger denotes the Hermitian transpose.
\mathbf{P}_a^{\perp} = \mathbf{I} - \mathbf{a}(\mathbf{a}^{\dagger} \mathbf{a})^{-1} \mathbf{a}^{\dagger} .