rajIndex -- finds the Rajchgot index of a permutation

Given a permutation in 1-line notation, finds its Rajchgot index, as defined in [PSW].

• [PWS]: O. Pechenik, A. Weigandt, and D. Speyer, "Castlenuovo--Mumford regularity of matrix Schubert varieties" (see arXiv:2111.10681).

i1 : w = {7,2,5,8,1,3,6,4}

o1 = {7, 2, 5, 8, 1, 3, 6, 4}

o1 : List

i2 : rajIndex w

o2 = 21

i3 : v = {1,6,9,2,4,7,3,5,8}

o3 = {1, 6, 9, 2, 4, 7, 3, 5, 8}

o3 : List

i4 : rajIndex v

o4 = 21