ODE change of variable. Independent variable

given an ode

\[ \frac {d^{2}}{d t^{2}}y \left (t \right )+y \left (t \right ) = 2 t \]

do change of variable \(t=\tau + \pi \)

restart; 
ode:=diff(y(t),t$2)+y(t)=2*t; 
PDEtools:-dchange({t=tau+Pi},ode,known={t},unknown={tau},params=Pi)

\[ \frac {d^{2}}{d \tau ^{2}}y \left (\tau \right )+y \left (\tau \right ) = 2 \tau +2 \pi \]

it is important to use params=Pi. Watch what happens if we do not do that

restart; 
ode:=diff(y(t),t$2)+y(t)=2*t; 
PDEtools:-dchange({t=tau+Pi},ode,known={t},unknown={tau});

\[ \frac {d^{2}}{d \tau ^{2}}y \left (\tau , \pi \right )+y \left (\tau , \pi \right ) = 2 \tau +2 \pi \]

Which is not what we want.