def ode(x,r,xc):    
    """
    Compute the slope of a coordinate in an circle 
    Params:
        x = the coordinate of desire slop 
        r = radius of the slope 
        xc = x coordinate of the center 
        
    return: 
        slop of at the coordinate provided 
    """
    return -(r**2 - (x - xc)**2)**(-0.5)*(-1.0*x + 1.0*xc)
    #%%