ellipse               package:ellipse               R Documentation

_M_a_k_e _a_n _e_l_l_i_p_s_e

_D_e_s_c_r_i_p_t_i_o_n:

     A generic function returning an ellipse or other outline of a
     confidence region for two parameters.

_U_s_a_g_e:

     ellipse(x, ...)
     ellipse.default(x, scale = c(1, 1), centre = c(0, 0), level = 0.95, 
         t = sqrt(qchisq(level, 2)), which = c(1, 2), npoints = 100, ...)

_A_r_g_u_m_e_n_t_s:

       x: An object. In the default method the parameter 'x' should be
          a correlation between -1 and 1 or a square positive definite
          matrix at least 2x2 in size. It will be treated as the
          correlation or covariance  of a multivariate normal
          distribution. 

     ...: Descendant methods may require additional parameters. 

   scale: If 'x' is a correlation matrix, then the standard deviations
          of each parameter can be given in the scale parameter.  This
          defaults to 'c(1, 1)', so no rescaling will be done. 

  centre: The centre of the ellipse will be at this position. 

   level: The confidence level of a pairwise confidence region.  The
          default is 0.95, for a 95% region.  This is used to control
          the size of the ellipse being plotted.  A vector of levels
          may be used. 

       t: The size of the ellipse may also be controlled by specifying
          the value of a t-statistic on its boundary.  This defaults to
          the appropriate value for the confidence region. 

   which: This parameter selects which pair of variables from the
          matrix will be plotted.  The default is the first 2. 

 npoints: The number of points used in the ellipse.  Default is 100. 

_D_e_t_a_i_l_s:

     The default method uses the  '(cos(theta + d/2), cos(theta -
     d/2))' parametrization of an ellipse, where  'cos(d)' is the
     correlation of the parameters.

_V_a_l_u_e:

     An 'npoints' x '2' matrix is returned with columns named according
     to the row names of the matrix 'x' (default ''x'' and ''y''),
     suitable for plotting.

_R_e_f_e_r_e_n_c_e_s:

     Murdoch, D.J. and Chow, E.D. (1996). A graphical display of large 
     correlation matrices. The American Statistician 50, 178-180.

_S_e_e _A_l_s_o:

     'ellipse.lm', 'ellipse.nls',  'ellipse.profile',
     'ellipse.profile.nls', 'ellipse.arima0', 'plotcorr'

_E_x_a_m_p_l_e_s:

     # Plot an ellipse corresponding to a 95% probability region for a
     # bivariate normal distribution with mean 0, unit variances and 
     # correlation 0.8.
     plot(ellipse(0.8), type = 'l')

