Oscar Rothaus, a Cornell University professor of mathematics who, during the Cold War, helped develop a vital military mathematical tool that simulates physical processes, died in Ithaca on May 24. He was 75.

Today the mathematical tool is used in speech recognition systems and for analyzing DNA. However, Rothaus helped develop the tool, called the Hidden Markov Model, or HMM, for military purposes as a member of the Communication Research Division at the Defense Department's Institute for Defense Analyses (IDA) in Princeton, N.J., in the early 1960s. The model was declassified in the early 1970s.

The HMM helped to usher in an era of high technology, allowing scientists to determine probabilities and to develop and improve PET (positron emission tomography) scans. HMM also allows scientists to compare strands of DNA with an entire genetic library. The mathematical model also is used in speech recognition systems, and it could have future uses in the analysis of robotics and as an aid in musical analysis.

Rothaus' other mathematical research included combinatorics and coding theory, Lie and Jordan algebras, and Sobolev and logarithmic Sobolev inequalities.

A native of Baltimore, Rothaus earned his bachelor's degree (1948), master's degree (1950) and doctorate (1958) from Princeton University. He served in the U.S. Army Signal Corps during the Korean War from 1951 to 1953. From 1953 to 1960, he was a mathematician at the National Security Agency in Washington, D.C. He joined the IDA in 1960, becoming its deputy director in 1963. He became a visiting professor of mathematics at Yale University in 1965.

Rothaus joined the Cornell faculty as a professor in 1966 and served as the mathematics department chair from 1973 to 1976. In 1995 he became acting department chair. Rothaus was a visiting professor at Hebrew University in Jerusalem, the University of Strasbourg in France and King's College London.

He is survived by his wife, Tobe Barban; his daughters, Carla of Brookline, Mass., Ruth Caston of Davis, Calif., and Tamar of Buffalo, N.Y.; and five grandchildren.

In lieu of flowers, the family requests that memorial donations be sent to Cornell Plantations.