Abstract
We compute the numerical index of the two-dimensional real space for
and
, where
is the root of
and
. This, together with the previous results in Merí and Quero [On the numerical index of absolute symmetric norms on the plane. Linear Multilinear Algebra. 2021;69(5):971–979] and Monika and Zheng [The numerical index of
. Linear Multilinear Algebra. 2022;1–6. Published online DOI:10.1080/03081087.2022.2043818], gives the numerical index of the two-dimensional real
space for
.
KEYWORDS:
Acknowledgments
The authors thank the referees for carefully reading the manuscript and for their comments which led to an improved version of this paper.
Disclosure statement
No potential conflict of interest was reported by the author(s).