  We study the quantum effects on the Coulomb branch of N=2 SU(2)
supersymmetric Yang-Mills with fundamental matters compactified on R^3 x S^1,
and extract the explicit perturbative and leading non-perturbative corrections
to the moduli space metric predicted from the recent work of Gaiotto, Moore and
Neitzke on wall-crossing [1]. We verify the predicted metric by computing the
leading weak coupling instanton contribution to the four fermion correlation
using standard field theory techniques, and demonstrate perfect agreement. We
also demonstrate how previously known three dimensional quantities can be
recovered in appropriate small radius limit, and provide a simple geometric
picture from brane construction.
