ellipse3d                package:rgl                R Documentation

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

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

     A generic function and several methods returning an ellipsoid or
     other outline of a confidence region for three parameters.

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

     ellipse3d(x, ...)
     ## Default S3 method:
     ellipse3d(x, scale = c(1, 1, 1), centre = c(0, 0, 0), level = 0.95, 
                 t = sqrt(qchisq(level, 3)), which = 1:3, subdivide = 4, ...)
     ## S3 method for class 'lm':
     ellipse3d(x, which = 1:3, level = 0.95, t = sqrt(3 * qf(level, 
                                                     3, x$df.residual)), ...)     
     ## S3 method for class 'glm':
     ellipse3d(x, which = 1:3, level = 0.95, t, dispersion, ...) 
     ## S3 method for class 'nls':
     ellipse3d(x, which = 1:3, level = 0.95, t = sqrt(3 * qf(level, 
                                                     3, s$df[2])), ...) 

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

       x: An object. In the default method the parameter 'x' should be
          a  square positive definite matrix at least 3x3 in size. It
          will be treated as the correlation or covariance  of a
          multivariate normal distribution. 

     ...: Additional parameters to pass to the default method or to
          'qmesh3d'. 

   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, 1)', so no rescaling will be done. 

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

   level: The confidence level of a simulataneous confidence region. 
          The default is 0.95, for a 95% region.  This is used to
          control the size of the ellipsoid. 

       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 variables from the object will
          be plotted.  The default is the first 3. 

subdivide: This controls the number of subdivisions (see
          'subdivision3d') used in constructing the ellipsoid.  Higher
          numbers give a smoother shape. 

dispersion: The value of dispersion to use.  If specified, it is
          treated as fixed, and chi-square limits for 't' are used. If
          missing, it is  taken from 'summary(x)'. 

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

     A 'qmesh3d' object representing the ellipsoid.

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

     # Plot a random sample and an ellipsoid of concentration corresponding to a 95% 
     # probability region for a
     # trivariate normal distribution with mean 0, unit variances and 
     # correlation 0.8.
     if (require(MASS)) {
       Sigma <- matrix(c(10,3,0,3,2,0,0,0,1), 3,3)
       Mean <- 1:3
       x <- mvrnorm(1000, Mean, Sigma)
       
       open3d()
       
       plot3d(x, size=3, box=FALSE)
       
       plot3d( ellipse3d(Sigma, centre=Mean), col="green", alpha=0.5, add = TRUE)
     }  

     # Plot the estimate and joint 90% confidence region for the displacement and cylinder
     # count linear coefficients in the mtcars dataset

     data(mtcars)
     fit <- lm(mpg ~ disp + cyl , mtcars)

     open3d()
     plot3d(ellipse3d(fit, level = 0.90), col="blue", alpha=0.5, aspect=TRUE)

