Product integral

The expression "product integral" is used informally for referring to any product-based counterpart of the usual sum-based integral of classical calculus. The first product integral was developed by the mathematician Vito Volterra in 1887 to solve systems of linear differential equations. (Please see "Type II" below.) Other examples of product integrals are the geometric integral ("Type I" below), the bigeometric integral, and some other integrals of non-Newtonian calculus.