A matrix of satisfying A= A2 is called idempotent matrix.It is an idempotent element of matrix ring Mn(F).A matrix of satisfying r(A)= r(A2) is called rank-idempotent matrix.They are closely related to decomposition of space and invariant subspace.Some pr
idempotent matrixrank-idempotent matrixkernel of matrixcolumn space of matrixrank of matrix