We study the inverse problem of determining the magnetic field and the electric potential entering the Schrödinger equation in an infinite 3D cylindrical domain, by Dirichlet-to-Neumann map. The cylindrical domain we consider is a closed waveguide in the sense that the cross section is a bounded domain of the plane. We prove that the knowledge of the Dirichlet-to-Neumann map determines uniquely, and even Hölderstably, the magnetic field induced by the magnetic potential and the electric potential. Moreover, if the maximal strength of both the magnetic field and the electric potential, is attained in a fixed bounded subset of the domain, we extend the above results by taking finitely extended boundary observations of the solution, only.Keywords: Inverse problem, magnetic Schrödinger equation, Dirichlet-to-Neumann map, infinite cylindrical domain.1.3. State of the art. Inverse coefficients problems for partial differential equations such as the Schrödinger equation, are the source of challenging mathematical problems, and have attracted many attention over the last decades. For instance, using the Bukhgeim-Klibanov method (see [14,35,36]), [3] claims Lipschitz stable determination of the time-independent electric potential perturbing the dynamic (i.e. non stationary) Schrödinger equation, from a single boundary measurement of the solution. In this case, the observation is performed on a sub boundary fulfilling the geometric optics condition for the observability, derived by Bardos, Lebeau and Rauch in [2]. This geometrical condition was removed by [8] for potentials which are a priori known in a neighborhood of the boundary, at the expense of weaker stability. In the same spirit, [22] Lipschitz stably determines by means of the Bughkgeim-Klibanov technique, the magnetic potential in the Coulomb gauge class, from a finite number of boundary measurements of the solution. Uniqueness results in inverse problems for the DN map related to the magnetic Schrödinger equation are also available in [24], but they are based on a different approach involving geometric optics (GO) solutions. The stable recovery of the magnetic field by the DN map of the dynamic magnetic Schrödinger equation is established in [9] by combining the approach used for determining the potential in hyperbolic equations (see [5,7,11,28,44,47,49]) with the one employed for the idetification of the magnetic field in elliptic equations (see [23,45,50]). Notice that in the one-dimensional case, [1] proved by means of the boundary control method introduced by [4], that the DN map uniquely determines the time-independent electric potential of the Schrödinger equation. In [10] the time-independent electric potential is stably determined by the DN map associated with the dynamic magnetic Schrödinger equation on a Riemannian manifold. This result was recently extended by [6] to simultaneous determination of both the magnetic field and the electric potential. As for inverse coefficients problems of the Schrödinger equation with either Neumann, spectral, or scatte...