\[\mathbf{B}=\begin{bmatrix}\alpha_{1}&\beta_{2}&&&0\\
\beta_{2}&\alpha_{2}&\beta_{3}&&\\
&\ddots&\ddots&\ddots&\\
&&\beta_{n-1}&\alpha_{n-1}&\beta_{n}\\
0&&&\beta_{n}&\alpha_{n}\end{bmatrix}\]