def threept_center(x1, x2, x3, y1, y2, y3):
    """
    Calculates center coordinate of a circle circumscribing three points
    
    Parameters
    --------------
    x1: `double`
        First x-coordinate 
    x2: `double`
        Second x-coordinate 
    x3: `double`
        Third y-coordinate 
    y1: `double`
        First y-coordinate 
    y2: `double`
        Second y-coordinate 
    y3: `double`
        Third y-coordinate 
    
    Returns
    ----------
    double, double:
        Returns center coordinates of the circle. Return None, None if the determinant is zero
    
    """
    
    determinant = 2*( (x3-x2)*(y2 - y1) - (x2 - x1)*(y3-y2) )
    
    if determinant < 0.1:
        return None, None
    
    
    x_numerator = (y3 - y2)*(x1**2 + y1**2) + (y1 - y3)*(x2**2 + y2**2) + (y2 - y1)*(x3**2 + y3**2)
    y_numerator = (x3 - x2)*(x1**2 + y1**2) + (x1 - x3)*(x2**2 + y2**2) + (x2 - x1)*(x3**2 + y3**2)
    
    xc = x_numerator/(2*determinant)
    yc = -y_numerator/(2*determinant)
    
    return xc, yc