Produit matriciel

$\begin{array}{rl}
   &
   \begin{matrix}
     \phantom{g1} C_1 & C_2 & \cdots & C_j & \cdots & C_q
   \end{matrix} \\
   B = &
   \begin{pmatrix}
     b_{11} & b_{12} & \cdots & b_{1j} & \cdots & b_{1q} \\
     \vdots & \vdots & & & \vdots \\
     b_{i1} & b_{i2} & \cdots & b_{ij} & \cdots & b_{iq} \\
     \vdots & \vdots & & & \vdots \\
     b_{p1} & b_{p2} & \cdots & b_{pj} & \cdots & b_{pq}
   \end{pmatrix} \\
   A =
   \begin{matrix}
     L_1 \\ L_2 \\ \vdots \\L_i \\ \vdots \\ L_p
   \end{matrix}
   \begin{pmatrix}
     a_{11} & a_{12} & \cdots & a_{1j} & \cdots & a_{1p} \\
     a_{21} & a_{22} & \cdots & a_{2j} & \cdots & a_{2p} \\
     \vdots & \vdots & & & \vdots \\
     a_{i1} & a_{i2} & \cdots & a_{ij} & \cdots & a_{ip} \\
     \vdots & \vdots & & & \vdots \\
     a_{n1} & a_{n2} & \cdots & a_{nj} & \cdots & a_{np}
   \end{pmatrix} &
   \begin{pmatrix}
     c_{11} & c_{12} & \cdots & c_{1j} & \cdots & c_{1q} \\
     c_{21} & c_{22} & \cdots & c_{2j} & \cdots & c_{2q} \\
     \vdots & \vdots & & & \vdots \\
     c_{i1} & c_{i2} & \cdots & c_{ij} & \cdots & c_{iq} \\
     \vdots & \vdots & & & \vdots \\
     c_{n1} & c_{n2} & \cdots & c_{nj} & \cdots & c_{nq} \\
   \end{pmatrix} = A \times B
 \end{array}$