home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
OS/2 Shareware BBS: 10 Tools
/
10-Tools.zip
/
octa21eb.zip
/
octave
/
SCRIPTS.ZIP
/
scripts
/
statistics
/
base
/
qqplot.m
< prev
next >
Wrap
Text File
|
1997-02-19
|
2KB
|
77 lines
## 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: [q, s] = qqplot (x [, dist [, params]])
##
## Performs a QQ-plot (quantile plot).
##
## If F is the CDF of the distribution `dist' with parameters `params'
## and G its inverse, and x a sample vector of length n, the QQ-plot
## graphs ordinate s(i) = i-th largest element of x versus abscissa q(i)
## = G((i - 0.5)/n).
##
## If the sample comes from F except for a transformation of location
## and scale, 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 quantile plot of the uniform distribution on
## [2,4] and x, use `qqplot (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 QQ-plot (quantile plot)
function [q, s] = qqplot (x, dist, ...)
if (nargin < 1)
usage ("qqplot (x [,dist [,params]])");
endif
if !(is_vector(x))
error ("qqplot: x must be a vector.");
endif
s = sort (x);
n = length (x);
t = ((1 : n)' - .5) / n;
if (nargin == 1)
f = "stdnormal_inv";
else
f = sprintf ("%s_inv", dist);
endif;
if (nargin <= 2)
q = feval (f, t);
q_label = f;
else
param_string = sprintf ("%g", va_arg ());
for k = 2 : (nargin - 2);
param_string = sprintf ("%s, %g", param_string, va_arg ())
endfor
q = eval (sprintf ("%s (t, %s);", f, param_string));
q_label = sprintf ("%s with parameter(s) %s", f, param_string);
endif
if (nargout == 0)
xlabel (q_label);
ylabel ("sample points");
set nokey;
plot (q, s);
endif
endfunction