假设 X ∈ R m × n X \in \R^{m \times n} X∈Rm×n,通常在数据降维过程中m<<n
令 A = X T X A=X^TX A=XTX, B = X X T B=XX^T B=XXT,显然 A ∈ R n × n A \in \R^{n \times n} A∈Rn×n, B ∈ R m × m B \in \R^{m \times m} B∈Rm×m, r a n k ( A ) = r a n k ( B ) rank(A)=rank(B) rank(A)=rank(B),显然,A和B都是对称半正定矩阵,且A有n个特征向量,B有m个特征向量。
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