Finding norms of Hadamard multipliers Original Research Article

The norm of a matrix B as a Hadamard multiplier is the norm of the map X at X · B, where is the Hadamard or entrywise product of matrices. Watson proposed an algorithm for finding lower bounds for the Hadamard multiplier norm of a matrix. It is shown how Watsonʹs algorithm can be used to give upper bounds as well, which, in many cases, yield the Hadamard multiplier norm to any desired accuracy. A sharp form of Wittstockʹs decomposition theorem is proved for the special case of Hadamard multiplication.