def  cobbdouglas(x, par):
    """ Cobb douglas utility function for 2 goods.
    
    INPUT:
    
    Parameters
    par (alpha) : relative preference for consumption to leisure, 0<alpha<1
    
    Consumption bundle
    x           : Consumption tuple
      x[0]      : consumption
      x[1]      : leisure

    OUTPUT
    u           : utility (negative)"""
    
    c=x[0]
    l=x[1]
    alpha=par
    
    u= (c**alpha)*l**(1-alpha)
    return -u