Past exam of the options I course of the University of Oxford / 2013 / P / 2 / b / Solution

The elimination multipliers are $m_{21}=2$, $m_{31}=4$, and $m_{32}=3$. The unit lower triangular matrix in the LU factorization is thereforeDirect multiplication checksThe positive signs in $L$ undo the row subtractions used during Gaussian elimination.