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Let's call (r_i)_{i>=0} the sequence of the ranks of (A^i)_{i>=0}. | |
For any i>=0, the image of A^{i+1} is a subspace of the image of A^{i}. | |
Our sequence of ranks (r_i) is non-increasing. | |
Since Im(A^{i+1}) ⊂ Im(A^i), if there exists i such that r_i = r_{i+1}, Im(A^{i+1}) = Im(A^i). | |
From this, it follows that Im(A^k) = Im(A^i) (k > i), or r_k = r_i. | |
In other words, (r_i) is a sequence of non-negative integers that | |
- starts at n | |
- might be stricly decreasing for a while |