# 9.4 Matrices

## Explanation

A matrix is a rectangular arrangement that is a convenient way to organize data in a table format of rows and columns. Individual items in a matrix are referred to as entries or as elements. One use of enlarged brackets is to enclose a matrix and to show matrix lines. In the print version of a matrix, vertical lines define the left and right margins of the matrix. Since matrices are to be arranged in a vertical format, it is important to align the enlarged opening and closing brackets and the left side of each column within the matrix. Identifiers, signs of comparison, signs of operation, or punctuation that appear outside of the matrix are placed on the first braille line. This occurs even though they may be centered in the print version. Each row of the matrix begins with an opening enlarged bracket and ends with a closing enlarged bracket. Values that appear before the closing enlarged bracket are not adjacent to the bracket. This is necessary in order to achieve vertical alignment.

## Enlarged brackets

The enlarged brackets are three-cell symbols. Dot four is used to indicate the bracket modification; dot six, the capitalization indicator, to signify enlargement; and the opening or closing sign of grouping.

## Rules for brailling matrices

To braille a matrix, first determine the number of cells required for the longest line in the table. Based upon the length of the longest line, determine where the opening and closing brackets and the first item in each column should begin within each row. This is to ensure vertical alignment. Matrices are spatial arrangements. As in all spatial arrangements, leave a blank line above and below each matrix, unless it begins at the top of a page or ends at the bottom of a page.

Each column is to be left justified; that is, the first characters of entries in each column are vertically aligned. If, for example, one of the entries in a column contains a signed number and others do not: position the plus or minus sign in vertical alignment with the numeric indicators which are the left-most characters in other entries of the same column. This may require leaving spaces between an item and a closing bracket.

A column of blank braille cells is inserted between the entry columns.

The numeric indicator must precede all numerals, even if they are adjacent to, or in contact with, an opening bracket.

Each opening bracket must be in contact with the first entry in a row. This occurs whether that entry is a numeral with its numeric indicator, or another mathematical symbol such as a dollar sign.

Opening and closing brackets must be aligned in a column. All enclosure symbols are to be brailled as enlarged brackets, not vertical lines.

At least one row of the matrix must have a closing bracket in direct contact with the last entry in a row.

Use space-saving techniques to confine the matrix to one braille page. If a row is longer than a braille line and thus must be continued on the next line as a runover: begin and end the lines that run over with opening and closing bracket symbols, aligned with any other runover brackets; indent the runover entry two braille cells; do not skip lines between rows.

Material outside the matrix, such as identifiers, signs of comparison, signs of operation, or punctuation, are to be placed on the first braille line of the display. This rule is followed even if these characters are centered in print.

There are no exercises for this lesson due to its spatial nature.