  Relativistic equations of Bethe-Salpeter type for hadron structure are most
conveniently formulated in momentum space. The presence of confining
interactions causes complications because the corresponding kernels are
singular. This occurs not only in the relativistic case but also in the
nonrelativistic Schr\"odinger equation where this problem can be studied more
easily. For the linear confining interaction the singularity reduces to one of
Cauchy principal value form. Although this singularity is integrable, it still
makes accurate numerical solutions difficult. We show that this principal value
singularity can be eliminated by means of a subtraction method. The resulting
equation is much easier to solve and yields accurate and stable solutions. To
test the method's numerical efficiency, we performed a three-parameter
least-squares fit of a simple linear-plus-Coulomb potential to the bottomonium
spectrum.
