Matrix Formulas

$\textbf{A}_{n,m}\textbf{B}_{m,p} = \textbf{C}_{n,p} $ Matrix mult result size; also cols A must equal rows B
$\textbf{M}_{i,j}^T = \textbf{M}_{j,i} $ Matrix transpose
$\textbf{M} = [\textbf{a} \textbf{b} \textbf{c}]$ Column vector representation
$\textbf{M} = \begin{bmatrix}
X & a & b \\
a & X & c \\
b & c & X
\end{bmatrix} $ Symmetric matrix (X is be any value)
$\textbf{M}^T = \textbf{M}$  
$\textbf{M} = \begin{bmatrix}
0 & a & b \\
-a & 0 & c \\
-b & -c & 0
\end{bmatrix}$ Antisymmetric matrix or skew-symmetric matrix (diagonals must be 0)
$\textbf{M}^T = -\textbf{M}$  
$\textbf{M}\textbf{v} = v_x \textbf{a} + v_y \textbf{b} + v_z \textbf{c}$ Column vector mult notation (a,b,c cols of M)
$\begin{vmatrix}a & b \\ c & d \end{vmatrix} = ad - bc$ 2D Matrix determinant
$det(\textbf{M}) = \sum\limits_{i=0}^{n-1} M_{ik}(-1)^{i+k}\vert\textbf{M}_{\bar{ik}}\vert $ Recursive determinant (each $\vert M_{ik}\vert$ is the sub matrix excluding the current col)
  k is chosen as any row; good when row is mostly zeros
$C_{ij}(\textbf{M}) = (-1)^{i+j}\vert\textbf{M}_{\bar{ij}}\vert$ Cofactor matrix definition
$\textbf{M}^{-1} = \frac{1}{det(\textbf{M})} \textbf{C}^T(\textbf{M})$ Inverse; $C^T(M) =$ adjugate matrix
$\textbf{A}^{-1} = \frac{1}{A_{00}A_{11} - A_{01}A_{10}}
\begin{bmatrix}
A_{11} & -A_{01} \\
-A_{10} & A_{00}
\end{bmatrix}$ 2D Matrix inverse
$\textbf{B}^{-1} = \frac{1}{det(\textbf{B})}
\begin{bmatrix}
B_{11}B_{22} - B_{...
...{20} & B_{01}B_{20} - B_{00}B_{21} & B_{00}B_{11} - B_{01}B_{10}
\end{bmatrix} $ 3D Matrix inverse
$\textbf{M}^{-1} = \frac{1}{[\textbf{a},\textbf{b},\textbf{c}]}
\begin{bmatrix}...
...\textbf{c} \times \textbf{a} \\
\textbf{a} \times \textbf{b} \\
\end{bmatrix}$ 3D matrix inverse (a,b,c cols of M)
$\textbf{M}^{-1} = \frac{1}{\textbf{s} \cdot \textbf{v} + \textbf{t} \cdot \text...
...\times \textbf{c} - z\textbf{s} \vert \textbf{c} \cdot \textbf{s}
\end{bmatrix}$ 4D Matrix inverse. a,b,c,d = 3D column vectors of M.
  x,y,z,w = last row of M, x = $a \times b$, t = $c \times d$, u = $ya -xb$, v = $wc -zd$