The phrase "approximation of the underlying" is correct and usable in written English.
It can be used in contexts where you are discussing a simplified or estimated representation of a more complex or foundational concept.
Example: "The model provides an approximation of the underlying data trends, allowing for easier analysis."
Alternatives: "estimate of the fundamental" or "representation of the core".
To facilitate the observer design, the system dynamics is modeled by considering a linearized approximation of the underlying nonlinear dynamics around the subcritical uniform flow condition.
We show the existence and possible uniqueness of regression functions, discuss the stability of regression functions under perturbations and approximation of the underlying data, and propose an extension of the coefficient of determination R-squared for assessing the goodness of fit.
It is shown that reasonable simplifications according to the specific design and the typical operating conditions of compact plate heat exchangers together with a semi-discretization of the spatial domain by means of the finite volume method provides a compact finite-dimensional approximation of the underlying partial differential equations (pdes).
Thus an efficient symbolic solution, in comparison to the numerical approximation, of the underlying differential equation is obtained.
The full method [35] consisted of extracting the fMRI time series and deconvolving the seed's BOLD signal to gain an approximation of the underlying neuronal signal.
Each matrix represents an approximation of the underlying NN, but the matrix representation is computationally much faster than the computation of the NN directly.
The linear additive model often provides a reasonable approximation to the underlying statistical architecture of a complex trait and it is easy to interpret.
Models cast at a symbolic level are sometimes useful as high-level approximations of the underlying mechanisms of thought.
The nonlinearity complicates attempts to construct efficient and accurate numerical approximations of the underlying systems of equations.
This resemblance as well as the above derived asymptotic stability region (3.10) indicate that the fractional difference equation (1.1) could be a very suitable tool for numerical approximations of the underlying fractional differential equation.
One of the most common approaches to estimating demand relationships is based on a direct differential approximation of the demand function, which generates a set of equations that are local first-order approximations of the underlying relationship between prices, quantities and income (Okrent and Alston 2011).
