A procedure is needed that reduces the number of fluid equations into simpler form. Such as Reductive perturbation technique (RPT) is applied to nonlinear waves of small amplitudes and rescales space (r) and time (t) coordinates in the original system of equations. The objective of rescaling is to introduce slowness in space and time since unlike the fast sinusoidal oscillations of the linear model, nonlinear structures evolve slowly.

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several reasons.

1. Scale separation - For example, using stretched coordinates can isolate small-scale turbulence from large-scale fluid motion or focus on the edge of the plasma where gradients are steeper.

2.Non-uniformity of plasma parameters: Stretched coordinates allow for a more accurate representation of these non-uniformities, leading to a better understanding of the underlying physics and more accurate numerical simulations.

3. Improved numerical accuracy:stretched coordinates can provide better resolution in regions with steep gradients or rapid variations, such as plasma boundaries or sheared flows.

4. Simplification of equations: Sometimes, the use of stretched coordinates can simplify the governing equations by transforming them into a more convenient form.

5. Boundary conditions: Stretched coordinates can help in applying appropriate boundary conditions at the plasma edge, which is crucial for accurately modeling plasma behavior.

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Stretched coordinates are used in plasma physics, especially in fluid equations, to simplify the solution of nonlinear equations. They involve transforming the physical domain into a computational domain where the equations become easier to solve. Stretched coordinates provide benefits such as improved numerical stability, enhanced resolution in critical regions, and reduced effects of numerical diffusion or dispersion. Overall, they help researchers obtain more accurate and reliable solutions for complex plasma phenomena.

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