%% Copyright (C) 1995, 1996, 1997  Kurt Hornik
%%
%% This file is part of Octave.
%%
%% Octave 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.
%%
%% Octave 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 Octave; see the file COPYING.  If not, write to the Free
%% Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
%% 02110-1301, USA.

%% -*- texinfo -*-
%% @deftypefn {Function File} {[@var{pval}, @var{b}, @var{n}] =} signtest (@var{x}, @var{y}, @var{alt})
%% For two matched-pair samples @var{x} and @var{y}, perform a sign test
%% of the null hypothesis PROB (@var{x} > @var{y}) == PROB (@var{x} <
%% @var{y}) == 1/2.  Under the null, the test statistic @var{b} roughly
%% follows a binomial distribution with parameters @code{@var{n} = sum
%% (@var{x} ~= @var{y})} and @var{p} = 1/2.
%%
%% With the optional argument @code{alt}, the alternative of interest
%% can be selected.  If @var{alt} is @code{'~='} or @code{'<>'}, the
%% null hypothesis is tested against the two-sided alternative PROB
%% (@var{x} < @var{y}) ~= 1/2.  If @var{alt} is @code{'>'}, the
%% one-sided alternative PROB (@var{x} > @var{y}) > 1/2 ('x is
%% stochastically greater than y') is considered.  Similarly for
%% @code{'<'}, the one-sided alternative PROB (@var{x} > @var{y}) < 1/2
%% ('x is stochastically less than y') is considered.  The default is
%% the two-sided case.
%%
%% The p-value of the test is returned in @var{pval}.
%%
%% If no output argument is given, the p-value of the test is displayed.
%% @end deftypefn

%% Author: KH <Kurt.Hornik@wu-wien.ac.at>
%% Description: Sign test
%% Adapted for the use with M*tlab by AS <alois.schloegl@gmail.com> Dec 2006

function [pval, b, n] = signtest (x, y, alpha, alt)

  if ((nargin < 2) || (nargin > 4))
    error;
  end
  if nargin<3,
  	alpha=.05; 
  end; 

  if (~ (isvector (x) && isvector (y) && (length (x) == length (y))))
    error ('sign_test: x and y must be vectors of the same length');
  end

  n   = length (x);
  x   = reshape (x, 1, n);
  y   = reshape (y, 1, n);
  n   = sum (x ~= y);
  b   = sum (x > y);
  cdf = binocdf (b, n, 1/2);

  if (nargin == 2)
    alt  = '~=';
  end

  if (strcmp (alt, '~=') || strcmp (alt, '<>') || (alt==0))
    pval = 2 * min (cdf, 1 - cdf);
  elseif (strcmp (alt, '>') || (alt==1))
    pval = 1 - cdf;
  elseif (strcmp (alt, '<') || (alt==-1))
    pval = cdf;
  else
    error ('sign_test: option %s not recognized', alt);
  end

  if (nargout == 0)
    printf ('  pval: %g\n', pval);
  elseif nargout > 1,
    b = (pval<alpha);
  end

end
