**Pavel Grinfeld** (also known as **Greenfield**) is an applied mathematician. He is a member of the Mathematics department at Drexel University. He studies problems with moving surfaces in applied mathematics (particularly calculus of variations), geometry, physics, and engineering.

Grinfeld received his PhD in Applied Mathematics from the MIT in 2003. He spent two years as a postdoctoral fellow at the MIT Department of Earth, Atmosphere and Planetary Sciences, conducting research in geodynamics.

Grinfeld is the author of the dynamic fluid film equations.

Grinfeld is a co-author (with Haruo Kojima of Rutgers University) of the instability of the 2S electron bubbles.

Grinfeld currently teaches Linear Algebra, Differential Equations, and Tensor Analysis. He is the author of a textbook on Tensor Calculus (2013) as well as an e-workbook on linear algebra. He has recorded hundreds of video lectures; several dozen on Tensors (in a video course which may accompany his textbook) as well as over a hundred shorter videos on linear algebra. Many of these are available on YouTube as well as other sites.

Hydrodynamics and fluid films dynamics, thermodynamics and phase transformations, minimal surfaces and calculus of variations.

Grinfeld is the founder of Lemma, Inc. which has developed the online learning system also called Lemma (https://www.lem.ma). Lemma combines high-quality lectures on subjects ranging from Linear Algebra to Tensor Calculus with a rich variety of practice problems that are designed to provide the students with immediate feedback. The systems also includes a real-time messaging service that allows educators and students to connect in informal, yet informative sessions.