Benoit B. Mandelbrot, a maverick mathematician who developed an innovative theory of roughness and applied it to physics, biology, finance and many other fields, died on Thursday in Cambridge, Mass. He was 85. His death, at a hospice, was caused by pancreatic cancer, his wife, Aliette, said. He had lived in Cambridge. Dr. Mandelbrot coined the term “fractal” to refer to a new class of mathematical shapes whose uneven contours could mimic the irregularities found in nature. “Applied mathematics had been concentrating for a century on phenomena which were smooth, but many things were not like that: the more you...