## `linalg::row` -- extract rows of a matrix

#### Introduction

`linalg::row``(A, r)` extracts the r-th row vector of the matrix A.

#### Call(s)

`linalg::row(A, r)`
`linalg::row(A, r1..r2)`
`linalg::row(A, list)`

#### Parameters

`A` | - | an m x n matrix of a domain of category `Cat::Matrix`
`r` | - | the row index: a positive integer <= m
`r1..r2` | - | a range of row indices (positive integers <= m)
`list` | - | a list of row indices (positive integers <= m)

#### Returns

a single row vector or a list of row vectors; a row vector is a 1 x n matrix of category `Cat::Matrix(R)`, where R is the component ring of `A`.

#### Related Functions

`linalg::col`, `linalg::delCol`, `linalg::delRow`, `linalg::setCol`, `linalg::setRow`

#### Details

- `linalg::row``(A, r1..r2)` returns a list of row vectors whose indices are in the range `r1..r2`. If `r2 < r1` then the empty list `[]` is returned.
- `linalg::row``(A, list)` returns a list of row vectors whose indices are contained in `list` (in the same order).

#### Example 1

We define a matrix over Q:

    >> A := Dom::Matrix(Dom::Rational)(
         [[1, 1/5], [-3/2, 5], [2, -3]]
       )

                                  +-           -+
                                  |    1,  1/5  |
                                  |             |
                                  |  -3/2,  5   |
                                  |             |
                                  |    2,   -3  |
                                  +-           -+

and illustrate the three different input formats for the function `linalg::row`:

    >> linalg::row(A, 2)

                                    +-       -+
                                    | -3/2, 5 |
                                    +-       -+

    >> linalg::row(A, [2, 1, 3])

                     -- +-       -+  +-      -+  +-     -+ --
                     |  | -3/2, 5 |, | 1, 1/5 |, | 2, -3 |  |
                     -- +-       -+  +-      -+  +-     -+ --

    >> linalg::row(A, 2..3)

                           -- +-       -+  +-     -+ --
                           |  | -3/2, 5 |, | 2, -3 |  |
                           -- +-       -+  +-     -+ --

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