Computing Weight 2 Modular Forms of Level p2

For a prime p we describe an algorithm for computing the Brandt matrices giving the action of the Hecke operators on the space V of modular forms of weight 2 and level p2. For$p \equiv 3$mod 4 we define a special Hecke stable subspace V0of V which contains the space of modular forms with CM by the ring of integers of$\mathbb{Q}(\sqrt{-p})$and we describe the calculation of the corresponding Brandt matrices.