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- ## Copyright (C) 1995, 1996, 1997 Kurt Hornik
- ##
- ## This program is free software; you can redistribute it and/or modify
- ## it under the terms of the GNU General Public License as published by
- ## the Free Software Foundation; either version 2, or (at your option)
- ## any later version.
- ##
- ## This program is distributed in the hope that it will be useful, but
- ## WITHOUT ANY WARRANTY; without even the implied warranty of
- ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- ## General Public License for more details.
- ##
- ## You should have received a copy of the GNU General Public License
- ## along with this file. If not, write to the Free Software Foundation,
- ## 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
-
- ## usage: [p, y] = ppplot (x [, dist [, params]])
- ##
- ## Performs a PP-plot (probability plot).
- ##
- ## If F is the CDF of the distribution `dist' with parameters `params'
- ## and x a sample vector of length n, the PP-plot graphs ordinate y(i) =
- ## F (i-th largest element of x) versus abscissa p(i) = (i - 0.5)/n. If
- ## the sample comes from F, the pairs will approximately follow a
- ## straight line.
- ##
- ## The default for `dist' is the standard normal distribution. The
- ## optional argument `params' contains a list of parameters of
- ## `dist'. E.g., for a probability plot of the uniform distribution on
- ## [2,4] ans x, use `ppplot (x, "uniform", 2, 4)'.
- ##
- ## If no output arguments are given, the data are plotted directly.
-
- ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at>
- ## Description: Perform a PP-plot (probability plot)
-
- function [p, y] = ppplot (x, dist, ...)
-
- if (nargin < 1)
- usage ("ppplot (x [, dist [, params]])");
- endif
-
- if !is_vector (x)
- error ("ppplot: x must be a vector.");
- endif
-
- s = sort (x);
- n = length (x);
- p = ((1 : n)' - 0.5) / n;
- if (nargin == 1)
- F = "stdnormal_cdf";
- else
- F = sprintf ("%s_cdf", dist);
- endif;
- if (nargin <= 2)
- y = feval (F, s);
- else
- y = feval (F, s, all_va_args);
- endif
-
- if (nargout == 0)
- axis ([0, 1, 0, 1]);
- set nokey;
- plot (p, y);
- endif
-
- endfunction
-