Abstract
We formulate Bogoliubov theory for a weakly interacting Bose-Einstein condensate confined to a spherically symmetric harmonic-oscillator potential. The theory is solved numerically by diagonalizing a Hamiltonian that is second order in boson creation and annihilation operators with the aid of a symplectic transformation. At zero temperature, the number of noncondensate atoms is well approximated by a heuristic expression based on Bogoliubov theory for free atoms.