The phrase "approximation is used for" is correct and usable in written English.
It can be used when discussing the purpose or application of an approximation in various contexts, such as mathematics, science, or engineering.
Example: "In calculus, approximation is used for estimating the value of complex integrals."
Alternatives: "approximation serves to" or "approximation is applied to".
The performance bounds are usually used to obtain the approximated estimation, while the high SNR approximation is used for the investigation of diversity and coding gains.
In both cases it is shown that no more than the three lowest order product densities are necessary to approximate the cell age correlations when a closure approximation is used for calculating higher order total product densities.
A Darwin approximation is used for suppressing electromagnetic vacuum modes.
Third order zigzag approximation is used for the axial displacement.
The generalized gradient approximation is used for the exchange correlation potential.
A simple approximation is used for the choice of the slope of a step profile.
The drift-diffusion approximation was used for the calculation of I V and C V characteristics and the thermionic emission theory for the extraction of diode parameters.
For stable inversion of the non-minimum phase zeros, a time delay approximation and a zero phase approximation are used for design of ILC, and their attainable bandwidths are analyzed.
The dusty-gas model and D'Arcy's law are used to describe the diffusive and viscous mass transport in the adsorbing bed, respectively, and the local equilibrium assumption or the linear driving force approximation are used for the uptake rate.
The effective field method (EFM) and quasi-crystalline approximation are used for the calculation of phase velocity and attenuation factor of the mean wave field propagating through the composite.
Results from the Milstein approximation are used for the stochastic model.
