Extension of the Equal Ripple Theorem to the first Zolotarev problem on two complex intervals

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Let SeS_e and SpS_p be the two intervals in CC, and let te(s)/te(−s)t_e(s)/t_e(-s) and tp(s)/tp(−s)t_p(s)/t_p(-s) be solutions of the Zolotarev problems on SeS_e and SpS_p, respectively. The arrays bbda1bbda_1, bbda2bbda_2, and bbda3bbda_3 determine the intervals, while ll is the degree of tet_e and the degree of tpt_p is k−lk-l.

Extended Equal Ripple conjecture. There are infinitely many arrays bbda1,bbda2,bbda3bbda_1,bbda_2,bbda_3 for which there exists ll such that

max⁡Se∣te(s)te(−s)∣=max⁡Sp∣tp(s)tp(−s)∣.\max_{S_e}\left|\frac{t_e(s)}{t_e(-s)}\right|=\max_{S_p}\left|\frac{t_p(s)}{t_p(-s)}\right|.

If the stated condition

is valid, then $t=t_et_p$ solves the global Zolotarev problem

.

This proposes an extension of the Equal Ripple Theorem from real rational approximation on one interval to the first Zolotarev problem on two complex intervals. The source does not provide evidence that the conjecture has been resolved.

References

Primary source

Vladimir Druskin, Murthy Guddati and Thomas Hagstrom, “On generalized discrete PML optimized for propagative and evanescent waves”, arXiv:1210.7862 (2012).

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