Positivity in Complex Spaces and Its Application to Gershgorin Discs. C. Zenger — 1984 Numerische Mathematik
A Comparison of Some Bounds for the Nontrivial Eigenvalues of Stochastic Matrices. C. Zenger — 1972 Numerische Mathematik
Improved Difference Schemes for the Dirichlet Problem of Poisson's Equation in the Neighbourhood of Corners. C. Zenger; H. Gietl — 1978 Numerische Mathematik