Abstract
<jats:title>Abstract</jats:title> <jats:p>From 1980 until the end of his life in 2009, Paul Samuelson never lost interest in mathematical theory, continuing to work on issues arising from his earlier work. The topic to which he returned most frequently was the linear models of production that had been central to his mathematical theory in the 1950s. A small minority of economists retained its interest in these models, believing them to provide an alternative to orthodox economic theory. Samuelson devoted much time analyzing such models, arguing that many of the claims made were mistaken. He also continued his investigations into physics, continuing his attempt to use mathematics he had developed for economics to place thermodynamics on a sounder theoretical footing.</jats:p>