mitrices latex code example

Example 1: matrix latex

\begin{bmatrix}
1 & 2 & 3 \\
a & b & c \\
a & b & c \\
\end{bmatrix}

Example 2: latex pmatrix

Trying to typeset an inline matrix here
$\begin{pmatrix}
  a & b\\ 
  c & d
\end{pmatrix}$ 
but it looks too big, so let's try 
$\big(\begin{smallmatrix}
  a & b\\
  c & d
\end{smallmatrix}\big)$ 
instead.