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Questions about the properties of vector spaces and linear transformations, including linear systems in general.

7 votes

Status of the Hadamard Circulant conjecture

Craigen and Jedwab have indicated that the September 2011 revision of Hurley, Hurley & Hurley also has a flaw: https://www.sfu.ca/~jed/Papers/Craigen%20Jedwab.%20Circulant%20Hadamard%202.%20Preprint.p …
3 votes
Accepted

Norm of Moore-Penrose inverse of a product

Here’s a small counterexample involving two rank-deficient matrices $A$ and $B$: $$A = \left( {\begin{array}{*{20}c} 0 & { - 1} & 0 \\ 0 & 0 & 0 \\ 0 & { - 1} & 0 \\ \end{array}} \right), …
Mark Yasuda's user avatar