Commutative Diagrams in TeX

Paul Taylor

September 1992

Message sent to registered users in September 1992

This message brings news of the development of my TEX package for drawing "commutative" diagrams, which is now widely used in the category theory and theoretical computer science communities. It is being sent directly to all of the users I know of (who have requested it by electronic mail or FTP from me, or asked questions about it), but as I know the package has been passed on, I would be grateful if you would copy this message to anyone to whom you have given the package itself.
The package was originally advertised on the "types" and "categories" electronic mailing lists in July 1990. In the following eighteen months some fixing of bugs took place, but there was little substantial change.
Since April 1992, I have re-written most of the code, largely with a view to improving the geometrical layout of the diagrams. Before completing this work and calling it version 4, I would like some feedback from users.
One of the areas which I have neglected in the past (largely because TEX makes it so difficult) is diagonal arrows. The code for drawing these using LATEX line segments has been re-written: now the closest available slope is chosen automatically and the commands have names similar to the horizontals and verticals.
However to do a better job of diagonals (and in future to support curved lines) some extension to TEX is needed. Being extensions they are necessarily not standard. Three possibilities are: Besides diagonals, the code for adjusting horizontal and vertical arrows has been completely rewritten and does a much better job of the geometry. Many of the problems with alignment, positioning and gaps have been fixed automatically, and greater control is given to the user to adjust those which cannot be. There are also several new options for the placement of the finished diagram on the page.
Arrow commands are now declared in a much simpler way. The declaration

is now all that is needed to define the example \rCrossedInto in the manual, along with the corresponding left, down, up and diagonal commands. Another option makes a consistent selection of arrowheads for all arrows, from a choice of vee, LaTeX, curlyvee, triangle and blacktriangle.
So much for selling you the new version. The reason for mailing you and asking for comments before completing what I intend to do for version 4 is that I want to get feedback on the following questions: