def JaccardIndex(axial_auto, axial_validation):
    """
    Calculates the Jaccard Index / Tanimoto Index between 2 numpy ndarrays. DSC = (A and B) / (A or B)

    Input ndarrays must be boolean.

    From Jaccard's paper: Jaccard, Paul (February 1912). "THE DISTRIBUTION OF THE FLORA IN THE ALPINE ZONE.1". New Phytologist. 11 (2): 37–50. doi:10.1111/j.1469-8137.1912.tb05611.x

    """
    denom = (axial_auto.astype('bool') | axial_validation.astype('bool')).sum()
    num = (axial_auto.astype('bool') & axial_validation.astype('bool')).sum()
    return num/denom