## Copyright (C) 1996 John W. Eaton
##
## 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, 59 Temple Place - Suite 330, Boston, MA
## 02111-1307, USA.

## usage: [xb, yb] = bar (x, y)
##
## Given two vectors of x-y data, bar produces a `bar' graph.
##
## If only one argument is given, it is taken as a vector of y-values
## and the x coordinates are taken to be the indices of the elements.
##
## If two output arguments are specified, the data are generated but
## not plotted.  For example,
##
##   bar (x, y);
##
## and
##
##   [xb, yb] = bar (x, y);
##   plot (xb, yb);
##
## are equivalent.
##
## See also: plot, semilogx, semilogy, loglog, polar, mesh, contour,
##           stairs, gplot, gsplot, replot, xlabel, ylabel, title

## Author: jwe

function [xb, yb] = bar (x, y)

  if (nargin == 1)
    if (is_vector (x))
      len = 3 * length (x) + 1;
      tmp_xb = tmp_yb = zeros (len, 1);
      tmp_xb(1) = 0.5;
      tmp_yb(1) = 0;
      k = 1;
      for i = 2:3:len
        tmp_xb(i) = k-0.5;
        tmp_xb(i+1) = k+0.5;
        tmp_xb(i+2) = k+0.5;
        tmp_yb(i) = x(k);
        tmp_yb(i+1) = x(k);
        tmp_yb(i+2) = 0.0;
        k++;
      endfor
    else
      error ("bar: argument must be a vector");
    endif
  elseif (nargin == 2)
    if (is_vector (x) && is_vector (y))
      xlen = length (x);
      ylen = length (y);
      if (xlen == ylen)
        len = 3 * xlen + 1;
        tmp_xb = tmp_yb = zeros (len, 1);
        cutoff = zeros (1, xlen-1);
        for i = 1:xlen-1
          cutoff(i) = (x(i) + x(i+1)) / 2.0;
        endfor
        delta_p = cutoff(1) - x(1);
        delta_m = delta_p;
        tmp_xb(1) = x(1) - delta_m;
        tmp_yb(1) = 0.0;
	k = 1;
        for i = 2:3:len
          tmp_xb(i) = tmp_xb(i-1);
          tmp_xb(i+1) = x(k) + delta_p;
          tmp_xb(i+2) = tmp_xb(i+1);
	  tmp_yb(i) = y(k);
	  tmp_yb(i+1) = y(k);
	  tmp_yb(i+2) = 0.0;
          if (k < xlen)
            if (x(k+1) < x(k))
              error ("bar: x vector values must be in ascending order");
            endif
	    delta_m = x(k+1) - cutoff(k);
            k++;
            if (k < xlen)
              delta_p = cutoff(k) - x(k);
	    else
	      delta_p = delta_m;
            endif
	  endif
	endfor
      else
        error ("bar: arguments must be the same length");
      endif
    else
      error ("bar: arguments must be vectors");
    endif
  else
    usage ("[xb, yb] = bar (x, y)");
  endif

  if (nargout == 0)
    plot (tmp_xb, tmp_yb);
  else
    xb = tmp_xb;
    yb = tmp_yb;
  endif

endfunction
