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Document 119

How to break an expression across two or more lines

Version: 2.5, 3.x, 4.x, 5.x - Scientific WorkPlace & Scientific Word

Breaking mathematical equations across several lines becomes more difficult when the expression is enclosed in parentheses. If you place the expression in a display and press Enter where you want the line break to occur, the parentheses expand to encompass both lines.

This is because the program's expanding brackets form an object that cannot be broken across lines. When you place the insertion point within this object and press Enter, the program creates a matrix within the expanding brackets, which then extend to the height of the matrix.

Below, we suggest two methods of maintaining correctly sized brackets around an expression broken across several lines. Each method has advantages and disadvantages.

Method 1: Use empty brackets

To make a single bracket expand to encompass the height of its contents, you can create a pair of brackets with the single bracket you want on one side and an empty bracket on the other. Empty brackets appear on your screen as a vertical dotted line, but they don't appear in print. You can use the same technique to surround the parts of an equation broken over several lines. However, you must decide where to break the expression, and then break it by hand.

  1. Manually break the expression into two parts.
  2. Enclose each part within a pair of expanding brackets: use an empty bracket for the right end of the first sub-expression and for the left end of the second sub-expression.
  3. Correct the spacing to make the size of the starting and ending brackets similar:
    1. Correct the spacing in the first sub-expression by inserting a zero-width rule, which has height and depth but no width:
      1. Place the insertion point inside the first expression, just to the right of the left bracket.
      2. From the Insert menu, choose Spacingand then choose Rule.
      3. In the Rule dialog box, set the Lift to 0.
      4. Set the Width to 0.
      5. Set the Height to the maximum of the height above or below the baseline of any part of either sub-expression.
      6. Choose OK.
    2. Insert the same rule immediately to the left of the right bracket in the second sub-expression.
  4. Preview your document, then fine tune the height of the rules as necessary.

Method 2: Use TeX brackets

Instead of surrounding the expression with pairs of expanding brackets, use TeX's larger brackets at either end. Like any other character, TeX brackets exist as independent objects; they behave just like large versions of the brackets that you obtain by pressing the bracket keys on your keyboard. When you use TeX brackets, the enclosed expression is no longer a single unit.

The advantage to this method is that you can allow TeX to break the expression. Note that you can encourage TeX to break an expression at a given point by inserting an allowbreak (from the Insert menu, choose Spacing, then choose Break, then select allowbreak).

The disadvantages to this method are that you are limited to a fixed set of bracket sizes, you must use TeX fields, and those fields must be within math. Also, if you're working in a multi-line equation, you need to break the expression yourself. Finally, the screen appearance is not as nice as that generated by the first method, because the TeX field boxes are visible.

Here are the steps:

  1. Make sure the insertion point is in math.
  2. Enter the TeX command for the left bracket, then choose OK.
  3. Enter your expression.
  4. Enter the TeX command for the right bracket, then choose OK.

Last revised 02/16/06

This document was created with Scientific WorkPlace.



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