Matrices and Multi-case Functions

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X = \left ( \array{1 & x \\ 0 & 1} \right )

The array option \collayout is used to line up the columns.

f(x) = \left \{

\array{\arrayopts{\colalign{left center left}}

       0 & \text{when} & x < 0 \\
     x^2 & \text{when} & x \geq 0}

\right

Here, two nested arrays are used to create a block matrix. Note how the vertical and horizontal dotted lines are specified.

M = \left [

    \array{\arrayopts{\colalign{center center}
                      \collines{dashed}
                      \rowlines{dashed}       }

    \array{1 & x_1 & \cdots & x_1^n \\
           1 & x_2 & \cdots & x_2^n \\
           \vdots & & & \vdots \\
           1 & x_n & \cdots & x_n^n}      & 0 \\

                        0                 & 1}

    \right ]