Scripting the techexplorer Hypermedia Browser

Input mathematics with the expression editor

The expression editor is a Java applet for editing mathematical expressions that exemplifies the use of the techexplorer Java interface to the Document Object Model (DOM) API. With the expression editor you can use the keyboard and mouse to create and edit mathematical structures that have been created either for the purpose of displaying mathematics in a document or performing a scientific computation.

The design of the expression editor is distinguished by three interrelated subcomponents:

1. it is based on a hierarchy of mathematical objects that relates to both the graphical rendering of the mathematics on the printed page, and the interpretation of the formulas by a computational system;
2. it provides for WYSIWYG ("what-you-see-is-what-you-get") editing of mathematics by use of a single visual cue: a highlighted subexpression; and,
3. it correlates these mathematical objects with keyboard actions for purposes of insertion, deletion, and navigation.

In what follows we introduce the basic use of the expression editor by examining how to create a basic expression, use the arrow keys, insert and delete mathematical expressions, and perform matrix edit commands.

Before trying out the editor, please change the color and font to the recommendations given below. Once you've done that, you are ready to start editing equations!

Creating a Basic Expression

First here is how you create an expression from scratch. The expression editor first presents you with an empty box. You fill this box with the first character that you type from the keyboard. As you type in new characters, the highlight moves to the right.

The expression editor has a single visual clue: a highlighted current expression. Here is a summary of basic principles:

• An empty box denotes an expression to be filled in. Your initial expression is an empty box. In general, your expression may contain any number of empty boxes.

• The current expression is highlighted. Each new expression you type becomes the new current expression, i.e., becomes highlighted.

• Variables names have single alphabetic characters. Thus xy is interpreted as the product of two variables x and y.

• LaTeX control words are entered with a backslash. For LaTeX control words, type a backslash (\) then one or more leading alphabetic letters of its name. Use TAB to complete the word as far as possible, then any non-alphabetic character to accept that completion. Alternatively, right-click on the characters typed so far to get a context menu of choices for completions. Control words like \sum and \int create variable-sized operators.

• An open-parenthesis creates an empty enclosed expression. Typing an open parenthesis, bracket, or curly brace, creates an empty enclosed expression. Want to change them? Use the right/left-arrow keys to move to the delimiter then type a new one (use a dot "." if you want it invisible).

• A close-parenthesis wraps the highlighted expression in parentheses. Typing a closed parenthesis, bracket, or curly brace wraps the current expression with identical delimiters.

• Infix operators like % or + create an empty box for the second operand. Operator % creates a two-dimensional fraction with an empty box for denominator. Simlarly ^, _, and # create two-dimensional forms for powers, subscripts, and roots ( for an n root, type left-arrow to get its box ). Operators +, -, =, *, and / create no two-dimensional structure but give you an empty box for the right operand.

Arrow Keys

As is customary with text editors, the arrow keys move you in the direction indicated by the arrow. Left and right arrows move you systematically across the characters of the math expression. Up and down move from superscript to subscript, numerator to denominator, and so on. Adding the CTRL key, lets you navigate the math expression as a tree structure.

• CTRL+Left and CTRL+Right move across siblings. Adding CTRL to the left- and right-arrow keys moves the highlight to the left or right sibling of the current expression tree.

• CTRL+Up means larger. Type CTRL+up arrow to move the highlight to the parent of the current expression.

• CTRL+Down means smaller. Type CTRL+down arrow to move the highlight to a child of the current expression.

• CTRL+SHIFT+Right/Left means extend. When CTRL+SHIFT is held down when typing the right- or left-arrow, the highlight is extended in the direction of the arrow.

Insertion and Deletion

• New characters are always inserted to the right unless preceded by typing the INSERT key. The characters you type are always inserted to the right of the currently highlighted expression. If you must insert a character to the left, just type the INSERT prior to that typing that character.

• DELETE (or ALT + d ) and BACKSPACE (or ALT+b ) delete the current expression.
  • The DELETE key deletes the current expression and moves the highlight to the right.
  • The BACKSPACE key deletes the current expression and moves the highlight to the left.

• DELETE and BACKSPACE delete enclosing parentheses. Once you have an expression enclosed in any kind of left-right delimiters: parentheses, brackets, or curly braces, typing DELETE or BACKSPACE replaces the enclosed expresssion by the expression itself.

• Left- and right-arrow introduce insertion boxes. When positioned at the right-end of an expression, successive right-arrows create an insertion box that moves "up" one level at a time. Alternatively, left-arrow can be used to introduce an insertion box to the left of the expression.

Recomended techexplorer settings

• Colors recommendation: suggest light gray--bottom row, 3rd from right, in table of basic colors for Selection Background( Options...->Colors from context menu on the Expression Editor window)
• Font recommendation: Times New Roman 13 for normal and italic math (Options...-->Fonts from context menu on Expression Editor window).

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Send comments and questions to techexpl@us.ibm.com.
Visit the official techexplorer home page at http://www.software.ibm.com/techexplorer/.