finding the area using Shoelace Polygon formula

function area = shoelace (x,y)

n = length(x);

area = 0;

for i = 1 : n-1

    area = area + (x(i) + x(i+1)) * (y(i) - y(i+1));

end

area = abs(area)/2;

end

How do I assign the values of x and y and get the answer on the command windows.

Answer 1

[Aykut Satici]

I don't think that is quite the right formula.

http://en.wikipedia.org/wiki/Shoelace_formula

Using the correct formula, your function would be very similar:

function area = shoelace(x,y)

n = length(x);
xp = [x; x(1)];
yp = [y; y(1)];

area = 0;
for i = 1:n
    area = area + det([xp(i), xp(i+1); yp(i), yp(i+1)]);
end
area = 1/2*abs(area);

Then you can call this function with two vectors containing the vertices of any n-gon:

x = rand(100,1);
y = rand(100,1);
shoelace(x,y)

You can check the result by comparing it with MATLAB's built-in function "polyarea"

http://www.mathworks.com/help/matlab/ref/polyarea.html