Technical Terms Positive Definite Matrix: A symmetric (or Hermitian) matrix with all eigenvalues positive, ensuring properties such as stability and invertibility.

In this paper we treat the two-variable positive extension problem for trigonometric polynomials where the extension is required to be the reciprocal of the absolute value squared of a stable ...

The higher-order accuracy of flat-top kernel estimators typically comes at the sacrifice of the positive semidefinite property. Nevertheless, we show how a flat-top estimator can be modified to become ...