# Name of an inversion-like function for permutations

Let $\pi\in S_n$ be a permutation. Define $m_k=|\{i: \ i\leq k, \ \pi(i)>k\}|$. For example, if $\pi=(597216384)$, then it's $m$ vector is $m(\pi):=(m_1,m_2,\ldots,m_{n-1})=(1,2,3,3,2,2,1,1)$. Is there some commonly associated name for $m_k$? In particular, for the sum $M:=\sum_{k=1}^{n-1}m_k$? This function came out of a paper related to reduced words. Quoting the paper, starting from the identity permutation, convert this permutation to $\pi$ by means of adjacent transpositions. Then one can interpret $m_k$ as the least number of times one needs to apply an adjacent swap $(k,k+1)\rightarrow (k+1,k)$.

Also, is there some nice relation between $M,m_k$ and the number of inversions in a permutation: $L(\pi):=\sum_{k=1}^{n-1}L_k(\pi),$ where $L_k(\pi)=\{i:\ i\geq k, \ \pi(k)>\pi(i)\}$? In other words, is there a connection between $m$ vectors and Lehmer codes? If there are no obvious connections between $m_k$ and inversions, are there some crude bounds that one can deduce between $L$and $M$? It seems to me that if one starts with the identity, $M=L$ for the sequence of the first few adjacent transpositions and then they begin to differ.

My inspiration for the latter question is based on the known bijection between major index and inversions.

-