def Astat(delta, k, G, n):
    """
    delta: contig size
    k: reads mapped in contig
    G: total genome size
    n: total reads mapped to genome
    """
    return n * delta * 1. / G - k * ln2
delta: contig size
    k: reads mapped in contig
    G: total genome size
    n: total reads mapped to genome