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I am working with a very large system of non-linear, 1st order coupled ODEs which seem to be stiff. I have been trying to solve them via NDSolve with several methods, finding StiffnessSwitching to be the one that best fits my problem. However, for certain values of the parameters, Mathematica complains about not being able to obtain an explicit expression for the ODEs. I have been able to solve this by switching the Method to Method->{"EquationSimplification"->"Solve"}. However, when I do this, I cannot specify that I still want the numerical method to be StiffnessSwitching. I have tried to use Method->{"EquationSimplification"->"Solve", "StiffnessSwitching"}, but it doesn't work. How can I use these two methods (or, as I understand it, the method for solving the ODEs and the one that simplifies the expressions?

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Just set

Method -> {"TimeIntegration" -> "StiffnessSwitching", 
           "EquationSimplification" -> Solve}

BTW this is mentioned in Details and Options section of document of NDSolve/NDSolveValue, I admit this isn't immediately obvious, though.

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