backSpline              package:splines              R Documentation

_M_o_n_o_t_o_n_e _I_n_v_e_r_s_e _S_p_l_i_n_e

_D_e_s_c_r_i_p_t_i_o_n:

     Create a monotone inverse of a monotone natural spline.

_U_s_a_g_e:

     backSpline(object)

_A_r_g_u_m_e_n_t_s:

  object: an object that inherits from class 'nbSpline' or
          'npolySpline'.  That is, the object must represent a natural
          interpolation spline but it can be either in the B-spline
          representation or the piecewise polynomial one.  The spline
          is checked to see if it represents a monotone function. 

_V_a_l_u_e:

     An object of class 'polySpline' that contains the piecewise
     polynomial representation of a function that has the appropriate
     values and derivatives at the knot positions to be an inverse of
     the spline represented by 'object'.  Technically this object is
     not a spline because the second derivative is not constrained to
     be continuous at the knot positions.  However, it is often a much
     better approximation to the inverse than fitting an interpolation
     spline to the y/x pairs.

_A_u_t_h_o_r(_s):

     Douglas Bates and Bill Venables

_S_e_e _A_l_s_o:

     'interpSpline'

_E_x_a_m_p_l_e_s:

     require(graphics)
     ispl <- interpSpline( women$height, women$weight )
     bspl <- backSpline( ispl )
     plot( bspl )                   # plots over the range of the knots
     points( women$weight, women$height )