Triangular Matrix

$$L=\left[\begin{array}{ccccc}{\ell }_{1,1}& & & & 0\\ {\ell }_{2,1}& {\ell }_{2,2}& & & \\ {\ell }_{3,1}& {\ell }_{3,2}& \ddots & & \\ ⋮& ⋮& \ddots & \ddots & \\ {\ell }_{n,1}& {\ell }_{n,2}& \dots & {\ell }_{n,n-1}& {\ell }_{n,n}\end{array}\right]$$

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References