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+model VanDerPolOscillator
+ parameter Real mu "dampening strength";
+ Real x;
+ Real y;
+equation
+ der(x) = y;
+ der(y) = mu * y * (1 - x^2) - x;
+end VanDerPolOscillator;
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+
+The Van der Pol oscillator was originally proposed by the Dutch electrical
+engineer and physicist Balthasar van der Pol while he was working at
+Philips. Van der Pol found stable oscillations, which he subsequently
+called relaxation-oscillations and are now known as a type of limit cycle in
+electrical circuits employing vacuum tubes. When these circuits were driven
+near the limit cycle, they become entrained, i.e. the driving signal pulls the
+current along with it. Van der Pol and his colleague, van der Mark, reported in
+the September 1927 issue of Nature that at certain drive frequencies an
+irregular noise was deterministic chaos.
+
+The Van der Pol equation has a long history of being used in both the physical
+and biological sciences. For instance, in biology, Fitzhugh and Nagumo
+extended the equation in a planar field as a model for action potentials of
+neurons. The equation has also been utilised in seismology to model the two
+plates in a geological fault, and in studies of phonation to model the right
+and left vocal fold oscillators.
+
+## References
+
+* Wikipedia:
+ [Van der Pol oscillator](https://en.wikipedia.org/wiki/Van_der_Pol_oscillator)