I recently started the study of vector bundles on $\mathbb{P}^n$, and started to read Rao's article 'A family of vector bundles on $\mathbb{P}^3$'. There, there is a notion of spectrum of a vector bundle. I searched this in some other articles, even in the excellent book "Vector Bundles on Complex Projective Space" by Okonek, Schneider and Spindler, but I cannot find the definition of spectrum. 


Does anyone has any reference where I can find this?


Thank you so much.



Vector Bundles of small rank
It seems that the notion of spectrum of vector bundles used in Rao's article is defined in Section 3 of 


* C. Okonek and H. Spindler. Reflexive Garben vom Rang $r>2$ auf $\mathbb{P}^n$. Crelle Journal Reine Angew. Math. 344 (1983), pp. 38-64.


If you are having trouble reading German, I could give the definition here, but refrain from it now because it is rather lengthy. The basic idea of the definition is that for a reflexive sheaf with specified splitting type, the cohomology of the restriction of the sheaf to a generic line can be described in terms of cohomology of explicitly given vector bundles on that line. The spectrum is a series of numbers telling you exactly which vector bundle on the line you have to take.


