- William W. Hager and Delphine Mico-Umutesi, Error Estimation in Nonlinear Optimization, Journal of Global Optimization, 59 (2014), pp. 327–341 (DOI 10.1007/s10898-014-0186-y)
- William W. Hager and M. Seetharama Gowda, Stability in the presence of degeneracy and error estimation (Mathematical Programming, 85 (1999), pp. 181-192).
- GNU GENERAL PUBLIC LICENSE