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function a = polygon_area(x,y)
% AREA Area of a planar polygon.
% AREA(X,Y) Calculates the area of a 2-dimensional
% polygon formed by vertices with coordinate vectors
% X and Y. The result is direction-sensitive: the
% area is positive if the bounding contour is counter-
% clockwise and negative if it is clockwise.
%
% See also TRAPZ.
% Copyright (c) 1995 by Kirill K. Pankratov,
% kirill@plume.mit.edu.
% 04/20/94, 05/20/95
% Make polygon closed .............
x = [x(:); x(1)];
y = [y(:); y(1)];
% Calculate contour integral Int -y*dx (same as Int x*dy).
lx = length(x);
a = -(x(2:lx)-x(1:lx-1))'*(y(1:lx-1)+y(2:lx))/2;
a = abs(a);
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