Consider the m × n system of linear equations

$\mathbf{Ax=b}$ | (19) |

If m = n and A is not singular, Equation 19 possesses a unique solution and is referred to as a fully determined system of equations. When m > n (or m = n and A is singular), Equation 19 is an underdetermined system of equations. Otherwise, m < n and Equation 19 is an overdetermined system of equations.