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Verifying topological indices for higher-order rank deficiencies. (English) Zbl 1005.65049
Summary: It has been known how to use computational fixed point theorems to verify existence and uniqueness of a true solution to a system of nonlinear equations within a small region about an approximate solution. This can, be done in $$O(n^3)$$ operations, where $$n$$ is the number of equations and unknowns. However, these standard techniques are only valid if the Jacobi matrix for the system is nonsingular at the solution.
In previous work and a dissertation (of Dian), we have shown, both theoretically and practically, that existence and multiplicity can be verified in a complex setting, and in the real setting for odd multiplicity, when the rank defect of the Jacobi matrix at an isolated solution is 1. Here, after reviewing work to date, we discuss the case of higher rank defect. In particular, it appears that $$p$$-dimensional searches are required if the rank defect is $$p$$, and that the work increases exponentially in $$p$$.

##### MSC:
 65H10 Numerical computation of solutions to systems of equations 65G30 Interval and finite arithmetic 65G20 Algorithms with automatic result verification
##### Software:
INTERVAL_ARITHMETIC; INTOPT_90
Full Text:
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