A non-linear differential equation is simply a differential equation where some non-linearity is applied to either the inputs or the outputs of the equation.
Related Journals of Nonlinear Differential Equations
Applied Mathematics Research express, Journal of Physical Mathematics, Research & Reviews: Journal of Statistics and Mathematical Sciences, Biometrics & Biostatistics Journal, Complex Analysis and Operator Theory, Proceedings of the Annual Symposium on Computational Geometry and Annual Reports in Computational Chemistry.
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