Louis Nirenberg, a mathematician who explored the complexities of equations commonly used by physicists and engineers, and who shared the 2015 Abel Prize, a top math award modeled after the Nobel Prize, died Jan. 26 in Manhattan. He was 94.

“It’s really hard to overstate how important Dr. Nirenberg was,” said Walter A. Strauss, an emeritus professor of mathematics and applied mathematics at Brown University. “He was one of the great mathematicians of the 20th century.” Dr. Nirenberg’s work focused on partial differential equations, which describe the vibrating of strings and drums, the flow of heat, the movement of water, and many other phenomena.

In 2015, Dr. Nirenberg and John F. Nash Jr., the mathematician whose life was depicted in the movie “A Beautiful Mind,” shared the Abel Prize for “striking and seminal contributions” to the field of partial differential equations.