1 ## Copyright (C) 1995-2012 Kurt Hornik
3 ## This file is part of Octave.
5 ## Octave is free software; you can redistribute it and/or modify it
6 ## under the terms of the GNU General Public License as published by
7 ## the Free Software Foundation; either version 3 of the License, or (at
8 ## your option) any later version.
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13 ## General Public License for more details.
15 ## You should have received a copy of the GNU General Public License
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20 ## @deftypefn {Function File} {[@var{p}, @var{y}] =} ppplot (@var{x}, @var{dist}, @var{params})
21 ## Perform a PP-plot (probability plot).
23 ## If F is the CDF of the distribution @var{dist} with parameters
24 ## @var{params} and @var{x} a sample vector of length @var{n}, the
25 ## PP-plot graphs ordinate @var{y}(@var{i}) = F (@var{i}-th largest
26 ## element of @var{x}) versus abscissa @var{p}(@var{i}) = (@var{i} -
27 ## 0.5)/@var{n}. If the sample comes from F, the pairs will
28 ## approximately follow a straight line.
30 ## The default for @var{dist} is the standard normal distribution. The
31 ## optional argument @var{params} contains a list of parameters of
32 ## @var{dist}. For example, for a probability plot of the uniform
33 ## distribution on [2,4] and @var{x}, use
36 ## ppplot (x, "uniform", 2, 4)
40 ## @var{dist} can be any string for which a function @var{dist_cdf}
41 ## that calculates the CDF of distribution @var{dist} exists.
43 ## If no output arguments are given, the data are plotted directly.
46 ## Author: KH <Kurt.Hornik@wu-wien.ac.at>
47 ## Description: Perform a PP-plot (probability plot)
49 function [p, y] = ppplot (x, dist, varargin)
56 error ("ppplot: X must be a vector");
61 p = ((1 : n)' - 0.5) / n;
65 F = str2func (sprintf ("%scdf", dist));
70 y = feval (F, s, varargin{:});
81 %% Test input validation
83 %!error ppplot (ones(2,2));