center.m

JAVA 数学程序库 提供常规的数值计算程序包

## 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.
##
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## 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
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## 02110-1301, USA.

## -*- texinfo -*-
## @deftypefn {Function File} {} center (@var{x})
## @deftypefnx {Function File} {} center (@var{x}, @var{dim})
## If @var{x} is a vector, subtract its mean.
## If @var{x} is a matrix, do the above for each column.
## If the optional argument @var{dim} is given, perform the above
## operation along this dimension
## @end deftypefn

## Author: KH <[e-mail]>
## Description: Center by subtracting means

function retval = center (x, varargin)

  if ((nargin != 1) && (nargin != 2))
    print_usage ();
  endif

  if (isvector (x))
    retval = x - mean (x, varargin{:});
  
  elseif (ismatrix (x))

    if (nargin < 2)
      dim = find (size (x) > 1, 1);

      if (isempty (dim)), 
	    dim=1; 
      endif;

    else
      dim = varargin {1};
    endif
    
    sz = ones (1, ndims (x));
    sz (dim) = size (x, dim);
    retval = x - repmat (mean (x, dim), sz);

  elseif (isempty (x))
    retval = x;
  else
    error ("center: x must be a vector or a matrix");
  endif

endfunction

/*
@GROUP
statistics
@SYNTAX
center(x,dim)
@DOC
Substract center value along the chosen dimension
@EXAMPLES
<programlisting>
center([2,3,5,3],2)
</programlisting>
@SEE
std, var, cov
*/