/usr/share/octave/packages/geometry-1.7.0/geom2d/isParallel.m is in octave-geometry 1.7.0-1build1.
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## Copyright (C) 2004-2011 INRA - CEPIA Nantes - MIAJ (Jouy-en-Josas)
## Copyright (C) 2012 Adapted to Octave by Juan Pablo Carbajal <carbajal@ifi.uzh.ch>
## All rights reserved.
##
## Redistribution and use in source and binary forms, with or without
## modification, are permitted provided that the following conditions are met:
##
## 1 Redistributions of source code must retain the above copyright notice,
## this list of conditions and the following disclaimer.
## 2 Redistributions in binary form must reproduce the above copyright
## notice, this list of conditions and the following disclaimer in the
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## AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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## CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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## -*- texinfo -*-
## @deftypefn {Function File} {@var{b} = } isParallel (@var{v1}, @var{v2})
## @deftypefnx {Function File} {@var{b} = } isParallel (@var{v1}, @var{v2},@var{tol})
## Check parallelism of two vectors
##
## @var{v1} and @var{v2} are 2 row vectors of length Nd, Nd being the dimension,
## returns @code{true} if the vectors are parallel, and @code{false} otherwise.
##
## Also works when @var{v1} and @var{v2} are two [NxNd] arrays with same number of
## rows. In this case, return a [Nx1] array containing @code{true} at the positions
## of parallel vectors.
##
## @var{tol} specifies the accuracy of numerical computation. Default value is 1e-14.
##
## Example
##
## @example
## isParallel([1 2], [2 4])
## ans =
## 1
## isParallel([1 2], [1 3])
## ans =
## 0
## @end example
##
## @seealso{vectors2d, isPerpendicular, lines2d}
## @end deftypefn
## FIXME or erase me
## Also works when one of @var{v1} or @var{v2} is scalar and the other one is [NxNd]
## array, in this case return [Nx1] results.
function b = isParallel(v1, v2, varargin)
# default accuracy
acc = 1e-14;
if ~isempty(varargin)
acc = abs(varargin{1});
end
# adapt size of inputs if needed
n1 = size(v1, 1);
n2 = size(v2, 1);
if n1 ~= n2
if n1 == 1
v1 = v1(ones(n2,1), :);
elseif n2 == 1
v2 = v2(ones(n1,1), :);
end
end
# performs computation
if size(v1, 2) == 2
b = abs(v1(:, 1) .* v2(:, 2) - v1(:, 2) .* v2(:, 1)) < acc;
else
# computation in space
b = vectorNorm(cross(v1, v2, 2)) < acc;
end
endfunction
%!assert (isParallel ([1 2], [2 4]))
%!assert (!isParallel ([1 2], [1 3]))
%!error (isParallel (3, rand(4,2)))
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