Curvature of a class of indefinite globally framed f-manifolds

We present a compared analysis of some properties of indefinite almost S-manifolds and indefinite S-manifolds. We give some characterizations in terms of the Levi-Civita connection and of the characteristic vector fields. We study the sectional and \phi-sectional curvature of indefinite almost S- manifolds and state an expression of the curvature tensor field for the inde- finite S-space forms. We analyse the sectional curvature of indefinite S- manifold in which the number of the spacelike characteristic vector fields is equal to that of the timelike characteristic vector fields. Some examples are also described.