paragraph_text: <td><math>\begin{matrix} \mathbf{\hat r}        & = & \frac{\rho}{r}\boldsymbol{\hat \rho}+\frac{   z}{r}\mathbf{\hat z} \\ \boldsymbol{\hat\vartheta} & = & \frac{z  }{r}\boldsymbol{\hat \rho}-\frac{\rho}{r}\mathbf{\hat z} \\ \boldsymbol{\hat\varphi}  & = & \boldsymbol{\hat\varphi} \end{matrix}</math>