The J^1 index calculates the Shannon Entropy of a tree, where at each node with two children, the Shannon Entropy is the sum of p_i log_2(p_i) over the two children i, and p_i is L / (L + R), where L and R represent the number of tips connected to the two daughter branches.
j_one(input_obj)
j^1 index
phylo object or ltable
Jeanne Lemant, Cécile Le Sueur, Veselin Manojlović, Robert Noble, Robust, Universal Tree Balance Indices, Systematic Biology, Volume 71, Issue 5, September 2022, Pages 1210–1224, https://doi.org/10.1093/sysbio/syac027