where .
 Differentiating and setting 
 gives the van der Pol
 equation. The equation
with the 
 replaced by 1 is sometimes also called the Rayleigh differential equation (Birkhoff
 and Rota 1978, p. 134; Zwillinger 1997, p. 126).
where .
 Differentiating and setting 
 gives the van der Pol
 equation. The equation
with the 
 replaced by 1 is sometimes also called the Rayleigh differential equation (Birkhoff
 and Rota 1978, p. 134; Zwillinger 1997, p. 126).
Weisstein, Eric W. "Rayleigh Differential Equation." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/RayleighDifferentialEquation.html