  \begin{align*}
\boldsymbol{\beta}_{t+1} &=  \boldsymbol{\beta}_{t} -  B^{-1} \cdot \nabla_{\boldsymbol{\beta}} l(\boldsymbol{\beta}), \\
 &=  \boldsymbol{\beta}_{t} -  \left[ \begin{array}{cccc}
 b_{00}    & 0  &  \ldots  & 0  \\
 0  &   b_{11}  &  \ldots  & 0  \\
 \vdots  & \vdots  & \ddots  & \vdots  \\
 0  &  0  &  \ldots  &  b_{dd}  \\
 \end{array}
 \right] \cdot \left[ \begin{array}{c}
 \nabla_{0}  \\
 \nabla_{1}  \\
 \vdots      \\
 \nabla_{d}  \\
 \end{array}
 \right]
 =  \boldsymbol{\beta}_{t} -  \left[ \begin{array}{c}
 b_{00} \cdot \nabla_{0}  \\
 b_{11} \cdot \nabla_{1}  \\
 \vdots      \\
 b_{dd} \cdot \nabla_{d}  \\
 \end{array}
 \right], %\\
 \end{align*}
