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Published online by Cambridge University Press: 04 June 2019
Let $F$ be an algebraically closed field of characteristic
$0$ and let
$\operatorname{sp}(2l,F)$ be the rank
$l$ symplectic algebra of all
$2l\times 2l$ matrices
$x=\big(\!\begin{smallmatrix}A & B\\ C & -A^{t}\end{smallmatrix}\!\big)$ over
$F$, where
$A^{t}$ is the transpose of
$A$ and
$B,C$ are symmetric matrices of order
$l$. The commuting graph
$\unicode[STIX]{x1D6E4}(\operatorname{sp}(2l,F))$ of
$\operatorname{sp}(2l,F)$ is a graph whose vertex set consists of all nonzero elements in
$\operatorname{sp}(2l,F)$ and two distinct vertices
$x$ and
$y$ are adjacent if and only if
$xy=yx$. We prove that the diameter of
$\unicode[STIX]{x1D6E4}(\operatorname{sp}(2l,F))$ is
$4$ when
$l>2$.
Financially supported by the National Natural Science Foundation of China (Grant Nos. 11671164, 11271149).