Suppression of field projection error in EPA at low frequencies by augmentation method

A new stable augmented EPA (equivalence principle algorithm) scheme is proposed for multi-scale problems. By using charge densities as extra unknowns, all the operators in EPA are augmented into the new forms. This new scheme is constructed based on the high-order point sampling method. Numerical examples show that the field projection operators in augmented EPA scheme are free of low frequency breakdown. Field projection accuracy is stable in a wide frequency regime.