cross

(tmp_for_tar/misc/cross.m)

Function Synopsis

z = cross (x, y)

Help text

 z = cross (x, y)

 Computes the vector cross product of two 3-dimensional vectors.

 x and y may be Px3 (default) or 3xP. If x and y have same size, the
 result has same size as the arguments. If one argument is Px3 and the
 other 3xP, the size of the result will be Px3 unless if
 prefer_column_vectors is set.

 Created: 15 October 1994
 Adapted-By: jwe
 Further modified by etienne@isr.ist.utl.pt (1999).

Listing of function file tmp_for_tar/misc/cross.m

## z = cross (x, y)
## 
## Computes the vector cross product of two 3-dimensional vectors.
##
## x and y may be Px3 (default) or 3xP. If x and y have same size, the
## result has same size as the arguments. If one argument is Px3 and the
## other 3xP, the size of the result will be Px3 unless if
## prefer_column_vectors is set.

## Author: KH <Kurt.Hornik@ci.tuwien.ac.at>
## Created: 15 October 1994
## Adapted-By: jwe
## Further modified by etienne@isr.ist.utl.pt (1999).
##
## Copyright (C) 1995, 1996  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.

function z = cross (x, y)
  
  if (nargin != 2)
    usage ("cross (x, y)");
  endif

				# Don't fuss about row/column size
  ntog = 0 ;			# Number of toggled arguments
  if size(x,2) != 3 && size(x,1) == 3, 
    x = x.' ;
    ntog++;
  end
  if size(y,2) != 3 && size(y,1) == 3, 
    y = y.' ;
    ntog++;
  end
  if (size (x,2) == 3 && size (y,2) == 3)

    z = [x(:,2).*y(:,3) - x(:,3).*y(:,2),...
	 x(:,3).*y(:,1) - x(:,1).*y(:,3),...
	 x(:,1).*y(:,2) - x(:,2).*y(:,1)];

    ## Return column only if both args were columns, or one arg was
    ## column and prefer_column_vectors is set.
    if ntog == 2 || ( (ntog == 1) && ! prefer_column_vectors)
      z = z.';
    endif

  else
    error ("cross: both x and y must be 3-dimensional vectors");
  endif

endfunction