$$A=\left[\begin{array}{cccc}a_{11}&a_{12}&\cdots&a_{1n}\\a_{21}&a_{22}&\cdots&a_{2n}\\\vdots&\vdots&\ddots&\vdots\\a_{m1}&a_{m2}&\cdots&a_{mn}\end{array}\right]$$

• $m$行$n$列の行列$A$の型は$(m\times n)$型
• 行列$A$の$(i, j)$成分（$i$行$j$列成分）は$a_{ij}$ $$(A)_{ij}=a_{ij}$$
• 行列$A$の第$i$行は$$\left[\begin{array}{cccc}a_{i1}&a_{i2}&\cdots&a_{in}\end{array}\right]$$
• 行列$A$の第$j$列は$$\left[\begin{array}{c}a_{1j}\\a_{2j}\\\vdots\\a_{mj}\end{array}\right]$$