This manuscript introduces a new approach for increasing the efficiency of automatic differentiation (AD) computations for
estimating the first order derivatives comprising the Jacobian matrix of a complex large-scale computational model. The objective
is to approximate the entire Jacobian matrix with minimized computational and storage resources. This is achieved by finding
low rank approximations to a Jacobian matrix via the Efficient Subspace Method (ESM). Low rank Jacobian matrices arise in
many of today’s important scientific and engineering problems, e.g. nuclear reactor calculations, weather climate modeling,
geophysical applications, etc. A low rank approximation replaces the original Jacobian matrix J (whose size is dictated by the size of the input and output data streams) with matrices of much smaller dimensions (determined
by the numerical rank of the Jacobian matrix). This process reveals the rank of the Jacobian matrix and can be obtained by
ESM via a series of r randomized matrix-vector products of the form: Jq, and JT ω which can be evaluated by the AD forward and reverse modes, respectively.
Keywords Forward mode - reverse mode - efficient subspace method - low rank