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### Some remarks on operators preserving partial orders of matrices

Discussiones Mathematicae Probability and Statistics

Stępniak [Linear Algebra Appl. 151 (1991)] considered the problem of equivalence of the Löwner partial order of nonnegative definite matrices and the Löwner partial order of squares of those matrices. The paper was an important starting point for investigations of the problem of how an order between two matrices A and B from different sets of matrices can be preserved for the squares of the corresponding matrices A² and B², in the sense of the Löwner partial ordering, the star partial ordering,...

### On orderings induced by the Loewner partial ordering

Applicationes Mathematicae

The partial ordering induced by the Loewner partial ordering on the convex cone comprising all matrices which multiplied by a given positive definite matrix become nonnegative definite is considered. Its relation to orderings which are induced by the Loewner partial ordering of the squares of matrices is presented. Some extensions of the latter orderings and their comparison to star orderings are given.

### The generalization of some properties of universal matrices

Mathematica Applicanda

We consider an k x k universal matrix G introduced by Hellwig (1976). We analyze two problems: the nonsingularity of the matrix G and the sign-consistency of the elements of the vector r = (ri) and of the solutrion b = (bi) to the system Gb = r. Obtained results generalize the results presented by Kolupa (1977, 1980).

For a given square matrix $A\in {M}_{n}\left(ℝ\right)$ and the vector $e\in {\left(ℝ\right)}^{n}$ of ones denote by (A,e) the matrix ⎡ A e ⎤ ⎣ ${e}^{T}$ 0 ⎦ This is often called the saddle point matrix and it plays a significant role in several branches of mathematics. Here we show some applications of it in: game theory and analysis. An application of specific saddle point matrices that are hollow, symmetric, and nonnegative is likewise shown in geometry as a generalization of Heron’s formula to give the volume of a general simplex, as well as a conditions...