A column vector of size $m$ is an ordered list of $m$ numbers, which is written in order vertically, starting at the top and proceeding to the bottom. At times, we will refer to a column vector as simply a vector. Column vectors will be written in bold, usually with lower case Latin letter from the end of the alphabet such as $\vect{u}$, $\vect{v}$, $\vect{w}$, $\vect{x}$, $\vect{y}$, $\vect{z}$. Some books like to write vectors with arrows, such as $\vec{u}$. Writing by hand, some like to put arrows on top of the symbol, or a tilde underneath the symbol, as in $\underset{\sim}{\textstyle u}$. To refer to the entry or component of vector $\vect{v}$ in location $i$ of the list, we write $\vectorentry{\vect{v}}{i}$.