The RT booklovers convention is an annual festival of lust, sisterhood and marketing, attended by thousands of writers and readers of romance fiction. This year's edition, held in Chicago, featured nighttime revels with bare-chested male models and seminars with titles like Beyond the Bodice. But to see its real, throbbing center of passion, you had to jam into a packed room where dozens of authors were talking mathematics: the profit calculations behind the digital-driven phenomenon of self-publishing.
"Romance is hot," said speaker Mark Coker, one of the few men in a room full of women--some dressed in character in 19th century...