If we have LUP.we can solve the equations in (n2) LUP-SOLVE(L.U,π，b) 1 n=L.rows 2 let x be a new vector of length n 3 for iI to n 4 片=bxt-∑1ly 5 for i =n downto 1 6 =(0-∑=i+14x)/: 7 return x But,how can we get LUP?If we have LUP, we can solve the equations in Θ(n2 ) But, how can we get LUP?