Diagonal and off-diagonal blocks of positive definite partitioned matrices
arXiv:2307.02034
Abstract
We establish a sharp inequality between the blocks of positive partitioned matrices and conjecture a triangle type inequality for contractions: Given three contactions A,B,C, we conjecture that the constant c=3/4 is sharp in the triangle inequality |A+B+C| < cI + |A| +|B| + |C|.
Final version, to appear in LAA, 13 pages