  Holonomic equations are recursive equations which allow computing efficiently
numbers of combinatoric objects. R{\'e}my showed that the holonomic equation
associated with binary trees yields an efficient linear random generator of
binary trees. I extend this paradigm to Motzkin trees and Schr{\"o}der trees
and show that despite slight differences my algorithm that generates random
Schr{\"o}der trees has linear expected complexity and my algorithm that
generates Motzkin trees is in O(n) expected complexity, only if we can
implement a specific oracle with a O(1) complexity. For Motzkin trees, I
propose a solution which works well for realistic values (up to size ten
millions) and yields an efficient algorithm.
