Showing Mathematicians in Love by Rudy Rucker

Reality is never more unpredictable than when two mathematicians are in love with the same girl, and can change the world to get her. Bela and Paul, two wild young mathematicians, are friends and roommates, and both are in love with Alma, Bela's girlfriend. They fight it out by changing reality using cutting-edge math. The contemporary world they live in is not quite this one, but much like Berkeley, California, and the two graduate students are trying to finish their degrees and get jobs. It doesn't help that their unpredictable advisor Roland is a mad mathematical genius who has figured out a way to predict specific bits of the future that can cause a lot of trouble...and that he's starting to see monsters in mirrors. When Bela and Paul mess around with reality, all heaven and hell break loose. Those monsters of Roland's were really there, but who are they? This novel is a romantic comedy with a whole corkscrew of SF twists from the writer who twice won the Philip K. Dick Award for best SF novel.