
Preventing Certain Errors in Writing Formulas
From NeoWiki
You need to observe some rules to correctly display formulas and to prevent errors in writing systems, matrices, etc. NeoOffice Math marks these erros with a red question mark.
Contents 
Alignment of Various Elements in a Formula
To align correctly the elements of formulas or equations, you may use the matrix, stack, binom, newline commands and
 use the spaces which are writen ~ . If you want, you can put them in braces {~}.
 The number of spaces which are to be added depends on the terms of the formula and, sometimes, you will have to proceed by trial and error to get a good result.
or
 use the alignr et alignl commands.
 You can replace alignl with quotes "", that you must place before the term which needs to be left aligned.
The examples below show these various methods and some differences in the layout that they produce.
Alignment of Several Equations
Note : In writing matrices, a +, – or = sign, must be put in quotes, if it is an element of the matrix, i.e. if it is placed between two #s.
Command  Formula 

left lbrace binom{a+b+c+d=f+g}{alignr h+k=i{~~~~} } right none
 
a*(b+c)=ab+ac{~~~~} newline (a+c)*(b+d)=ab+cb+ad+cd
 
matrix {alignr a*(b+c)#"="#alignl ab+ac ##
alignr (a+c)*(b+d)#"="#ab+cb+ad+cd}
 
left lbrace matrix{alignr x+2y+5z#"="# "" 3 ##
alignr x + y~~~~~ #"="# "" 2##
alignr x~~~~ "–" 3z #"="# "" 1} right none
 
matrix{ x+y+z#"="#""t ##
alignr x+y#"="#""t–z##
alignr x#"="#tzy }
}
 
""x+y+z=t newline
""~~~x+y=tz newline
~~~~~~~x=tzy

Alignment of Addition, Substraction, or Multiplication Signs
Command  Formula 

a+b+c{~~~} newline ab+cd
 
~~~~a*(b+c) newline (a+c)*(b+d)
 
a=\[b+c+g+h+j+i+k+l+m+dotslow newline
""{~~~~}d+f\]

Avoiding Gaps
If you leave a location empty where Math is waiting for "something", you get an error message, i.e. a red question mark.
Empty Boxes in Matrices
In a matrix, if you want a box to remain empty, you need to place a space ~, `, or {} in it.
Command  Formula 

left ( matrix{I_n # ~ ## ~ # I_m}right )=I_{n+m}
 
left ( matrix{A_n # {}# {} ## {} # dotsdown # {} ## {}#{}# A_m}right )

Binary Operators
A term must be present on both sides of the =, <, ≤, >, ≥, +, –, * signs, and of the union and intersection of sets symbols.
 x+y={} and {}intersection _{i in I} %omega_i
Note – This last formula is not always satisfying. The intersection symbol is too small if the sets are named with capital letters. In order to fix that issue, a better method is described in this article in NeoWiki.