Difference between revisions of "Documentation/FAQ/Formula"

Revision as of 21:35, 14 June 2006

How can I get a left bracket without a right bracket?

Since brackets have a grouping function they must always match and be correctly nested.

To get a single bracket without a matching bracket partner you have to escape the bracket with a backslash. For example to get a "[" without a corresponding "]" you should enter "\[".

Thus to typeset the interval [3;8) you should enter \[3 ";" 8\). The quotation marks around the semicolon ensures that it is not typeset in italic. (You're right, this has nothing to do with brackets!)

For scalable brackets it is essential that left and right matches, since the content that the brackets encloses must be well defined.

In this case you can use the invisible bracket none to get a single bracket. For example to get a scalable "[" without a corresponding "]" you should enter left [ ... right none.

Thus to typeset File:001a.gifyou should enter x=left lbrace binom -5 3 right none.

I enter x^* to typeset x^*, but get an error message. Why?

The problem is that * is a binary operator, that is there has to be an expression on both sides of the symbol.

You either have to enter the expression x^{{}*{}} to avoid the error message, or you could type x^"*" as well, where the quotes will interprete the asterisk not as a binary operator but as a "standalone" symbol.

If you use this construction a lot you might want to define the symbol as a userdefined symbol. See <A HREF="012.html">FAQ #012</A>. If you have defined the * as a userdefined symbol, say %ast, you can enter x^%ast.

This answer applies to a lot of other symbols as well. Some operators, such as +, are unary, that is there only has to be an expression to the right of the symbol. To typeset x⁺ you can enter x^{+{}}< or, of course, x^"+".

When I enter one of the symbols #, & ,|,^ or _ I get an unexpected result or an error message. How can I use these symbols?

These symbols all have a special meaning in Math:

• The symbol # is used in stacks and matrices.
• The symbols & and | are used for logical and and logical or.
• The symbols ^ and _ are used for

subscripts and superscripts.

To use them in your formula you can put them in quotation marks, which means that you insert them as text.

If you want to use the symbol "|" you should consider whether the construction you need is one of the the following:

• a divides b is used to typeset a| b.
• abs a is used to typeset |a|.

When I enter 3xy the number 3 comes out in italics. Is this a bug?

Not really. What happens here is, that Math uses multi-letter variables, which are common in some disciplines, like economy. The rule is that a variable consists of a sequence of letters, numbers and dots (the first character can not be a dot).

So when you enter 3xy this is considered a variable - and variables are typeset in italics. The only odd thing here is, that a variable can start with a number.

The correct way to enter the expression if you mean 3 times x times y is 3 x y (with spaces between the characters).

How do I align my equations at the equality sign?

Currently Math does not have an alignment construction. Instead you can use a matrix.

For example to typeset the equation

you should enter the following:

matrix{
   alignr x+y # {}={} # alignl 2 ##
   alignr x   # {}={} # alignl 2-y
}

The empty braces around = are necessary because = is a binary operator and thus needs an expression on each side.

You can reduce the spacing around = if you change the inter-column spacing of the matrix:

• Select Format-Spacing
• Click 'Category' and chooseMatrixes in the pop-up menu.
• Now enter 0% under 'Column spacing'.

Here is another example using a different solution:

To typeset the equation

the trick is to use phantom as follows:

""3(x+4)-2(x-1)=3 x+12-(2 x-2) newline
""phantom {3(x+4)-2(x-1)}=3 x+12-2 x+2 newline
""phantom {3(x+4)-2(x-1)}=x+14

The effect of the empty quotation marks is to left justify the line - a line starting with text (even an empty text) will always be left justified.

You can replace "" with alignl.