The research adopts the Galerkin and Petrov–Galerkin spectral methods to analyze the effects of implicit–explicit Runge–Kutta (IMEX RK) time schemes on the stability, accuracy, precision, and efficiency of computations when used in numerical simulations of the diffusion, Burgers’, and magneto-hydrodynamic (MHD) equations. The maximum time steps suitable for the Galerkin and Petrov–Galerkin spectral methods are determined based on an analysis of the diffusion equation. It is shown that for the Petrov–Galerkin spectral method it is possible to use a time step size that is nearly three times as large as that of the Galerkin spectral method. The results of the relative error analysis of Burgers’ equation show that the IMEX RK schemes become more stable and accurate with an increase in the number of basis functions and smaller time steps, while the effect of higher viscosity leads to a decrease in relative errors. It is found that when the number of basis functions is large, the higher-order IMEX RK schemes in conjunction with the Petrov–Galerkin spectral method efficiently discretize time and space and achieve high accuracy at various viscosities due to their well-conditioned band matrices. In addition, the problem of the influence of magnetic fields on the efficiency of different IMEX RK schemes is considered within the framework of a two-dimensional MHD system by studying the evolution of small perturbations in a conducting fluid flow. The analyses show that the higher-order IMEX RK schemes provide enhanced stability and accuracy, while the lower-order schemes offer computational efficiency at the expense of some accuracy.
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