1. Armstrong, M., 1982, The problems with universal kriging: Centre de Géostatisque, Fountainebleau, N-784.
2. Armstrong, M. and Delfiner, P., 1980, Towards a more robust variogram: A case study on coal: Centre de Géostatisque, Fontainebleau, N-671.
3. Atkinson, K. E., 1978, An introduction to numerical analysis, John Wiley & Sons, New York.
4. Broyden, C. G., 1975, Basic matrices: Macmillan, London.
5. Cressie, N. and Hawkins, D. H., 1980, Robust estimators of the variogram: I: Jour. Math. Geol., v. 12, p. 115?126.