Other Macros For Naming Equations

We have already noted that TEX allows you to put equations on the left hand side of a line using the macro leqno. For this reason, we too need a version of the naming macros which do the same thing. The obvious name for such a macro would be leqn and it is invoked by typing leqn equation.name If you include this in an equation the number comes out on the left.

In addition to this obvious addition to the macro set there are macros meant to be used for the automatic numbering of aligned equations. To learn about aligned equations you should read in the TEXbook or in First Grade TEX. Assuming that you have done so, let me remind you how about how aligned equations are generated, in order to set the stage for explaining how the macros eqinsert, leqinsert, mideqn and midleqn work.

Aligned equations are, as the name implies, a set of equations which appear one after the other. In order to make the spacing between these equations look nice and in order to make them line up so as not to look messy PLAIN TEX introduces the macro eqalign. This macro produces a list of equations which are aligned with respect to some common feature of each equation, for example an = sign. As with single displayed equations TEX allows you to number these sets of equations as if they are a single equation by using the commands eqno, leqno. PHYZZX, too, is kind and permits exactly the same thing; to do this you use the commands eqn and leqn. Since eqalign is a macro whose argument is the text of the equations, the way to use eqn, etc. is to type them after the right } which closes the eqalign command. For example, typing $$ eqalign{ cos { pi over 6 } = & sqrt{3/4} cr cos{ pi over4} =& sqrt{1/2} cr cos{ pi over3} =& sqrt{8} cr } eqn trig $$ yields

$\displaystyle \eqalign$ $\displaystyle {\cos{\pi \over 6}\ = &\ \sqrt{3/4} \cr \cos{\pi\over 4}\ = &\ \sqrt{1/2} \cr \cos{\pi \over 3}\ =&\ \sqrt{8} \cr}$ $\displaystyle \eqn$ $\displaystyle \trig$

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