The inverses of the combinations of two idempotent matrices
Kezheng Zuo
Abstract
Kezheng Zuo
Abstract
The paper researches the inverses of combinations of two idempotent matrices P±Q,I-PQ,aP+bQ - cPQ - dQP(where P,Q are two idempotent matrices).It first proves a rank equality of the combinations of two idempotent matrices aP +bQ - cPQ (where a≠0,b≠0,P,Q are two idempotent matrices)by using elementary transformations of block matrices.Secondly,the explicit expressions of some invertible combinations P±Q,I-PQ,aP + bQ-cPQ-dQP(where P,Q are idempotent matrices) are obtained by using the properties of the invertibility of P-Q and projectors when P - Q is invertible.Those expressions describe some features of the combinations of two idempotent matrices.
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The paper researches the inverses of combinations of two idempotent matrices P±Q,I-PQ,aP+bQ - cPQ - dQP(where P,Q are two idempotent matrices).It first proves a rank equality of the combinations of two idempotent matrices aP +bQ - cPQ (where a≠0,b≠0,P,Q are two idempotent matrices)by using elementary transformations of block matrices.Secondly,the explicit expressions of some invertible combinations P±Q,I-PQ,aP + bQ-cPQ-dQP(where P,Q are idempotent matrices) are obtained by using the properties of the invertibility of P-Q and projectors when P - Q is invertible.Those expressions describe some features of the combinations of two idempotent matrices.
Key concepts: Idempotent matrix, Idempotence, Invertible matrix, Mathematics, Rank (graph theory), Combinatorics, Block (permutation group theory), Pure mathematics