def to_ic50(x, max_ic50=50000.0):
    """
    Convert regression targets in the range [0.0, 1.0] to ic50s in the range
    [0, 50000.0].
    
    Parameters
    ----------
    x : numpy.array of float

    Returns
    -------
    numpy.array of float
    """
    return max_ic50 ** (1.0 - x)