I am trying to build a Python code that solves a set of coupled differential equations which will be spatially discretized by the method of lines advancing in time. I am planning to use solve_ivp. In my problem, the conservation of species includes the product of gas density and mass fraction of species in the time derivative. My question is how do I handle multiple time-dependent variables in a single equation in solve_ivp?

one of the equations looks like

$$ \frac{\partial}{\partial t}\left(\varepsilon\rho_gY_i\right)+\mathrm{div}\left(\varepsilon\rho_gu_gY_i\right) = \mathrm{div}\left(D_\text{eff}\rho_g\overrightarrow{\mathrm{grad}}\left(Y_i\right)\right)+\dot{\omega_i} $$

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    $\begingroup$ See example Lotka-Volterra. It works in the same way. Stack them together in the output vector. Beware, that solve_ivp does not allow a matrix before the time derivative, such as $M \frac{d}{dt}f$ . $\endgroup$
    – Bort
    Commented Aug 1, 2023 at 6:49


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