“Admission,” the Tina Fey/Paul Rudd romantic comedy that opens in theaters today, is based on a 2009 novel by Jean Hanff Korelitz — and, like many book-to-movie projects, its story onscreen is quite different from the one on the page. (I read the book last week, and learned that, for example, something that’s revealed very early in the film — the fact that Portia, Fey’s character, placed an infant for adoption 18 years ago — is a very late development in the book. And both Fey’s and Rudd’s characters are quite different from the book: Portia is less in-her-head, more uptight, funnier; Rudd’s John plays a bigger role and in fact engineers the movie’s central conflict, whereas in the book he’s less central.) Though I don’t think “Admission” entirely succeeds at being the sort of rom-com-dramedy hybrid it’s aiming for, most of the script changes make sense, as screenwriter Karen Croner was trying to make visual a story that, on the page, mostly happens in Portia’s head. But I’ve always wondered how novelists feel when their books are dramatically changed for the screen. New York Magazine apparently wondered that too, and got Korelitz and Croner together for a chat. Very interesting reading, particularly for those intrigued by the idea of adaptation — which happens for the screenwriter (virtually no movies make it to to screen with their scripts intact) as well.