  We present an efficient program for the exact diagonalization solution of the
pairing Hamiltonian in spherical systems with rotational invariance based on
the SU(2) quasi-spin algebra. The basis vectors with quasi-spin symmetry
considered are generated by using an iterative algorithm. Then the Hamiltonian
matrix constructed on this basis is diagonalized with the Lanczos algorithm.
All non-zero matrix elements of the Hamiltonian matrix are evaluated "on the
fly" by the scattering operator and hash search acting on the basis vectors.
The OpenMP parallel program thus developed, PairDiagSph, can efficiently
calculate the ground-state eigenvalue and eigenvector of general spherical
pairing Hamiltonians. Systems with dimension up to 10$^{8}$ can be calculated
in few hours on standard desktop computers.
