Pattern Recognition第一节课ML都不会算了，呵呵，linear algebra忘得一塌糊涂，抓这个周末时间好好好好复习复习咯~
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1. Elementary row operations:
Replacement(Replace one row by the sum of itself and a multiple of another row.)
Interchange(Interchange two rows.)
Scaling(Multiply all entries in a row by a nonzero constant.)
Strictly speaking, in linear algebra, two matrices are row equivalent if one can be changed to the other by a sequence of elementary row operations.
2. The transpose of a matrix: 将矩阵的行和列换过来
3. Suppose A=[a b; c d], A^-1 A=I The determinant of A is det A = ad-bc. A is invertible if and only if det A != 0. 行列式符号是在矩阵两边加两个杠。
[A I] --> [I A^-1]
4. The rank of a matrix A, denoted by rank A, is the dimension of the column space of A. A is an invertible matrix if and only if rank A = 0