def _b_min_ ( bp ) :
    """Get min values for bernstein polynomials
    
    >>> p  = ...
    >>> mn = p.min()

    The  value is such that: mn <= p(x)  for all x_min<=x<x_max
    """
    b    = bp.bernstein() 
    pars = b .pars()
    return min ( pars )