The Mathieu transformations make up a subgroup of canonical transformations preserving the differential form
\sumipi\deltaqi=\sumiPi\deltaQi
The transformation is named after the French mathematician Émile Léonard Mathieu.
In order to have this invariance, there should exist at least one relation between
qi
Qi
pi,Pi
\begin{align} \Omega1(q1,q2,\ldots,qn,Q1,Q2,\ldotsQn)&=0\\ &{} \vdots\\ \Omegam(q1,q2,\ldots,qn,Q1,Q2,\ldotsQn)&=0 \end{align}
where
1<m\len
m=n