Algorithm for Calculation of Longitudinal Target Polarization

We suggest using the Lagrange polynomial interpolation to calculate the longitudinal polarization of the large COMPASS target with a length of 2x55 cm. The algorithm does not change the polarizations measured by the NMR sensors. In addition, it allows taking into account the influence of the microwave field on the nuclear polarization at the resonator boundaries. As a result, measurements of polarization at several points of a long target and knowledge of the cavity design allow one to obtain a more explicit analytical expression for the target polarization. The work is performed in the COMPASS collaboration at CERN.