A Simple Solution to Numbering Equations

PHYZZX has a macro eq which can take care of this chore for you automatically. All you have to do is type $$ x + y = { 2 over (x - y) } eqno eq $$ to get

x + y = $\displaystyle {2 \over (x-y)}$ $\displaystyle \eqno$ $\displaystyle \eq$

and you will have automatically generated an equation number. The question is, What sort of equation number will you generate ?. Once again, this is a question of style. If you are in the Phys.Rev. format, or in the default Nuclear Physics format then the equation label is of the form chapterlabel.equation number. Equations are numbered sequentially within each chapter, but when you change chapters the chapter number is increased by 1 and the equation number is reset to 1. If you have chosen the format with unnumbered chapters and sections, then eq will automatically generate sequential equation numbers. As far as we are concerned this is the most satisfactory way of numbering things. For short papers, i.e. those with only one chapter, choose the unnumbered chapter format and all of your equations will be numbered sequentially; for longer papers, i.e. those which call for dividing them into chapters, numbering the equations by their chapter and number within the chapter makes it easier to refer to them. Sometimes, however, either out of perversity or because a paper has many chapters but very few equations, an author wishes to choose the format with numbered chapters but sequential equation numbers. This will happen if, before entering the first equation in your paper you type the command sequentialequations Hence, in the default mode, typing $$ 7x + 11xˆ 2 = 50 eqno eq $$ $$ 3x + xˆ 3 = 85 eqno eq $$ $$ 4x + 8xˆ 7 = 12 eqno eq $$ $$ 7x + 4xˆ 2 = 0 eqno eq $$ $$ x + 21xˆ 5 = -5 eqno eq $$ yields =0

7x + 11x² = 50 $\displaystyle \eqno$ $\displaystyle \eq$

3x + x³ = 85 $\displaystyle \eqno$ $\displaystyle \eq$

4x + 8x⁷ = 12 $\displaystyle \eqno$ $\displaystyle \eq$

7x + 4x² = 0 $\displaystyle \eqno$ $\displaystyle \eq$

x + 21x⁵ = - 5 $\displaystyle \eqno$ $\displaystyle \eq$

If, however, you first type sequentialequations; then typing $$ 7x + 11xˆ 2 = 50 eqno eq $$ $$ 3x + xˆ 3 = 85 eqno eq $$ $$ 4x + 8xˆ 7 = 12 eqno eq $$ $$ 7x + 4xˆ 2 = 0 eqno eq $$ $$ x + 21xˆ 5 = -5 eqno eq $$ yields

7x + 11x² = 50 $\displaystyle \eqno$ $\displaystyle \eq$

3x + x³ = 85 $\displaystyle \eqno$ $\displaystyle \eq$

4x + 8x⁷ = 12 $\displaystyle \eqno$ $\displaystyle \eq$

7x + 4x² = 0 $\displaystyle \eqno$ $\displaystyle \eq$

x + 21x⁵ = - 5 $\displaystyle \eqno$ $\displaystyle \eq$

Since you are an astute reader you have no doubt noticed that what I have told you to this point only solves half of the problem. While eq automatically generates equation numbers which, each time you run the paper through TEX , are automatically updated to conform to the order in which they appear in the text, we have no a priori way of knowing what these numbers are. The question is, How do we get hold of these numbers so that we can refer to them in the text? Well, eq provides a partial solution to this problem by definiing the control sequence ? a synonym for that number each time it is invoked. Hence, typing ? at any point in the text causes TEX to print the number of the last equation in which you used the command eq. For example by typing equation ? we cause TEX to print equation , which is the number of the last equation appearing in our examples. The only thing wrong with this solution is that the meaning of the symbol ? changes each time you invoke eq, so what happens if you want to refer back to an equation at several different points in the text?