Linear Equivalence of Full Weight Spectrum Cyclic Orbit Codes

Abstract

We determine the linear-equivalence classes within the two families of full weight spectrum one-orbit cyclic subspace codes. This solves the second open problem posed by Castello, Polverino and Zullo [J. Combin. Theory Ser. A 212 (2025) 106005]. For the first family, the criterion is a fractional linear transformation over $\F_q$ followed by a power of $q$-Frobenius. For the second family, it is an affine transformation over $\F_{q^2}$ together with a power of $q$-Frobenius. We use polynomial spaces over finite fields, the linear-isometry theorem for cyclic orbit codes, and trace duality. The arguments include parameters belonging to proper subfields of the ambient field.