Confusion about b in A2Q2

[kolyako1]

What is right-hand side vector b in question 2? It is described as a vector (which is one dimensional), but immediately it’s components are described by (i,1) and (i, m). This seems to imply that it is somehow two dimensional.

Do (i,1) and (i, m) represent something else for vector b? Is it not the i-th row of the first and m-th column?

[ccc]

The right-side vector is size n*m x 1 (column vector).
In the assignment, I refer to equation (i, j) as the equation
corresponding to cell (i, j), but I also give you to which component
of the vector it corresponds to (((i-1)m+j)).