Let S-0, ..., S-k be k + 1 similarity classes of matrices over an algebraic
ally closed field. This paper gives partial answers to the problems of exis
tence (recognition) and uniqueness module simultaneous similarity (rigidity
) of the solutions of the equation A(k) = A(0) + ... +A(k-1), with A(i) is
an element of S-i, 0 less than or equal to i less than or equal to k. (C) 1
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