iff( u)

A change of the dependent variable of the form u( r) = ¢>( r )v( r) with a suitable multiplier function </> is often used. A combination of the two methods with ¢>( r) equal to some power of r is frequently referred to as the Kelvin or Fowler transformation. The classical Emden-Fowler equation, with f(u) =uP, was reduced to an autonomous equation with such a technique by Fowler [6).