Solving the Richardson equations for fermions

Forty years ago Richardson showed that the eigenstates of the pairing Hamiltonian with constant interaction strength can be calculated by solving a set of nonlinear coupled equations. However, in the case of fermions these equations lead to singularities which made them very hard to solve. This paper explains how these singularities can be avoided through a change of variables making the fermionic pairing problem numerically solvable for arbitrary single-particle energies and degeneracies.