Two-dimensional system approximation using interval coefficients

We study the stability of a complex 2-D system characteristic polynomial g(s/sub 1/,s/sub 2/)=/spl Sigma//sub k1=0//sup m1//spl Sigma//sub k2=0//sup m2/ gk/sub 1/k/sub 2/s/sub 1//sup k1/s/sub 2//sup k2/ with interval coefficients g/sub k/1k/sub 2//spl isin/[g/sub -k1k2/,g/sub k1k2/] for each (k/sub 1/,k/sub 2/). It is hoped that such a study would be of help in ensuring the stability part of the approximation problem for 2-D systems with variable parameters. In order to solve the above problem, we derive Kharitonov (1979) type estremum polynomials for complex two-variable very strict Hurwitz interval polynomials.