def get_histogram_limits(filename):
    """Read a histogram file `filename' and return the smallest and largest values in the first column."""
    hmin = 0
    hmax = 0
    with open(filename, "r") as f:
        line = f.readline().split("\t")
        hmin = float(line[0])
        for line in f:
            line = line.split("\t")
            hmax = line[0]
    hmax = float(hmax)
    return (hmin, hmax)