What is the meaning of anaphora in linear algebra

What is the meaning of anaphora in linear algebra

In solving linear equations, the elimination of zeros of the elements below the main diagonal of the coefficient matrix belongs to elimination, and the elimination of zeros of the elements above the main diagonal of the coefficient matrix belongs to backstepping

Ask, in linear algebra "before generation" and "back generation" respectively mean? A little description

Previous generation: using two equations to eliminate an unknown quantity (such as x1)
It is equivalent to solving X1 with one equation and substituting the expression of X1 into another equation
Back to generation: the solution of the unknown into the equation to get other unknowns
If the equations are changed to
x1+x2+x3=2
x2-x3 = 1
X3 = 1, X2 = 1 by substituting 2, and X1 = 0 by substituting 1