  We give a new computational method to obtain symmetries of ordinary
differential equations. The proposed approach appears as an extension of a
recent algorithm to compute variational symmetries of optimal control problems
[Comput. Methods Appl. Math. 5 (2005), no. 4, pp. 387-409], and is based on the
resolution of a first order linear PDE that arises as a necessary and
sufficient condition of invariance for abnormal optimal control problems. A
computer algebra procedure is developed, which permits to obtain ODE symmetries
by the proposed method. Examples are given, and results compared with those
obtained by previous available methods.
