We give a computational algorithm for describing the one-dimensional cusps of the
Satake compactifications for the Siegel congruence subgroups in the case of degree
two for arbitrary levels. As an application of the results thus obtained, we calculate
the codimensions of the spaces of cusp forms in the spaces of modular forms of degree
two with respect to Siegel congruence subgroups of levels not divisible by
. We
also construct a linearly independent set of Klingen–Eisenstein series with respect to
the Siegel congruence subgroup of an arbitrary level.
Keywords
dimension formula, Siegel modular forms, Klingen–Eisenstein
series with level, cusp structure, double coset
decompositions
