The cause was acute pancreatitis, his son Igor said. Dr.
Arnold's work ranged widely across mathematics. He was a founder
of singularity theory, or, as it is sometimes more ominously
called, catastrophe theory. Singularity theory predicts that
under certain circumstances slow, smooth changes in a system can
lead to an abrupt major change, in the way that the slipping of
a few small rocks can set off an avalanche. The theory has
applications in physics, chemistry and biology. "He was a genius
and one of the greatest and most influential mathematicians of
our time," said Boris A. Khesin, a former student of Dr.
Arnold's and now a professor of mathematics at the University of
Toronto. One of Dr. Arnold's biggest contributions was applying
the methods of geometry and symmetry to the motion of particles.
Dr. Arnold work on how fluids flow was applied to the dynamics
of weather, providing a mathematical explanation for why it is
not possible to make forecasts months in advance. Infinitesimal
gaps or errors in infor