Loewner-monotonicity classification for differing parameter sequences

Determine whether the classification of continuously differentiable functions that are entrywise monotone in the Loewner order on each fixed-q Green family remains valid when the two Green matrices being compared have different parameter sequences q.

Background

The paper classifies continuously differentiable functions that satisfy the implication A\succeq B\Rightarrow f[A]\succeq f[B] when A and B belong to the same convex Green family obtained by fixing the parameter sequence q. The resulting functions are characterized through representations of their derivatives as positive mixtures of nonnegative real powers.

The conclusion explicitly identifies the unresolved extension in which the matrices A and B have different q-sequences. Establishing whether the same representation remains necessary and sufficient would extend the Loewner-monotonicity result beyond the fixed-parameter setting.

References

Whether the same classification holds when A and B have different parameter sequences q remains open.

Entrywise Positivity Preservers on Green Matrices  (2608.18491 - Xie, 19 Aug 2026) in Concluding remarks, Section 9

Preservers for Green matrices with zero entries or parameters, and preservers in a fixed dimension, remain to be studied.

Entrywise Positivity Preservers on Green Matrices  (2608.18491 - Xie, 19 Aug 2026) in Concluding remarks, Section 9