Abstract:
A matrix $A\in M_n(\mathbf C)$ is said to be accretive-dissipative if in its Hermitian decomposition
$$
A=B+iC, \quad B=B^*, \quad C=C^*,
$$
both matrices $B$ and $C$ are positive definite. Further, if $B=I_n$, then $A$ is called a Buckley matrix. The following extension of the classical Fischer inequality for Hermtian positive-definite matrices is proved.
Let
\begin{math}
A=\begin{pmatrix} A_{11}&A_{12} A_{21}&A_{22} \end{pmatrix}
\end{math}
be an accritive-dissipative matrix, $k$ and $l$ be the orders of $A_{11}$ and $A_{22}$, respectively, and let $m=\min\{k,l\}$. Then
$$
|{\det A}|\le3^m|{\det A_{11}}|\,|{\det A_{22}}|.
$$
For Buckley matrices, the stronger bound
$$
|{\det}|\le\biggl(\frac{1+\sqrt{17}}4\biggr)^m|{\det A_{11}}|\,|{\det A_{22}}|.
$$
is obtained.