Drode's Equations is a science-fiction short story written by fantasy/sci-fi/fiction writer Richard Grant. One of several short stories that he wrote early on, before his novels, it was written in 1981 and published in an anthology called The Ascent of Wonder: The Evolution of Hard SF, edited by David G. Hartwell and Kathryn Cramer. The story is in a sub-genre of science-fiction dealing largely with math (time in particular).
The short story is told from the first person point of view, in a style reminiscent of more archaic fiction. It appears to take place in a fictional setting, and uses fictional names, although treating them as if real. The main character (male, presumably) finds in his home an old notebook, which contains a set of equations so rare that they have become little more than legend. They are (he thinks) the work of Drode: hence Drode's equations. He sets off on a train, pondering the equations during his trip.
The equations are a set of three, and are supposed to be equivalent. Two of them are complex (the first especially, using a symbol for time frequently), the third very concise. Readers are led to ponder why the symbol for time appears often in the first, once in the second, and not at all in the third. Also, a symbol for motion or speed appeared only in the first and third equations. They seem to relate the same truth about Nature, in terms of Time as well as without Time.
The equations themselves are not given, and can only be pieced together in part from the text of the story.