  Well known to the machine learning community, the random feature model is a
parametric approximation to kernel interpolation or regression methods. It is
typically used to approximate functions mapping a finite-dimensional input
space to the real line. In this paper, we instead propose a methodology for use
of the random feature model as a data-driven surrogate for operators that map
an input Banach space to an output Banach space. Although the methodology is
quite general, we consider operators defined by partial differential equations
(PDEs); here, the inputs and outputs are themselves functions, with the input
parameters being functions required to specify the problem, such as initial
data or coefficients, and the outputs being solutions of the problem. Upon
discretization, the model inherits several desirable attributes from this
infinite-dimensional viewpoint, including mesh-invariant approximation error
with respect to the true PDE solution map and the capability to be trained at
one mesh resolution and then deployed at different mesh resolutions. We view
the random feature model as a non-intrusive data-driven emulator, provide a
mathematical framework for its interpretation, and demonstrate its ability to
efficiently and accurately approximate the nonlinear parameter-to-solution maps
of two prototypical PDEs arising in physical science and engineering
applications: viscous Burgers' equation and a variable coefficient elliptic
equation.
