Removal of the first derivative from a second-order differential equation (source code)

= Removal of the first derivative from a second-order differential equation

For
$$
y''+P(x)y'+Q(x)y=0,
$$
the substitution
$$
y=e^{-\frac12\int P(x)\,dx}v
$$
gives the normal form
$$
v''+\left(Q-\frac12P'-\frac14P^2\right)v=0.
$$