Ah, sorry: The patch is correct, but my explanation is wrong. Here's an update:
In inversion.pd this is realised by walking through the list with list-map. The interval to use next is calculated by taking the difference between the current element and the previous element. This interval is substracted (not added, because we are "retro"-grading) from the previous note, the resulting note is stored for the next step and inserted into the result list. The first element in a list is treated specially as it has no previous element: it's just copied and used as the starting note.
Frank and all,
Attached is an inversion.pd which is a bit simpler -- usually when inverting in pitch (rather than pitch-class) it's easier/simpler/better to invert with respect to an axis of symmetry rather than with respect to the first pitch in the series (of course you can assign the first pitch as the axis).
Meanwhile, if you're doing this with pitch-class instead of pitch (in other words transposing and inverting in a mod 12 universe, which is what you would probably be doing with 12-tone rows before assigning specific registers), instead of inverting with respect to an axis of symmetry, you invert with respect to the sum of the two pitch-classes in the original and inverted row -- sometimes called the "index" of inversion. The group theory is even cleaner if you think of transposition as an addition operator and inversion as a multiplication operator (in this case multiplication by 11, mod 12). If you're doing mod 12 operations, there is one more pitch operator -- multiplication by 5 or 7 -- which maps the chromatic scale to the circle of fifths and vice-versa. Then you can think of retrogression as "order inversion," and rotation, the other standard order-position operator, as "order transposition."
If you think it would be useful I can put together the standard 12-tone operators in mod 12 (or for that matter, an assignable modulus), but of course specific register information disappears. A more interesting but more difficult project would be to write a list abstraction to output the set-class of a given set of pitches, with an assignable modulus.
Matt