NOTATION
p：projection
vector
P：projection
matrix
e：error
vector
P：permutation
matrix
T：transport
sign
C(A)
：column
space
N(A)
：null space
U：upper
triangular
L：lower
triangula
rE：elimination
matrix
Q：orthogonal
matrix
, which means the column vectors are orthogonal
E：element
ary/elimination
matrix, which always appears in the elimination of matrix
N：null space matrix
, the “solution matrix” of AX=0
R：reduced matrix
, which always appears in the triangular matrix, “IF00”
I：identity matrix
S：eigenv ...