function pl = ploscina(A)
%pl = ploscina(A) vrne ploscino pl poligona, 
%ki je dan z zaporedjem tock 
%A = [A1, A2, ..., An].

%ploscina poligona brez tock je 0
pl = 0;
%sestejemo predznacene ploscine trikotnikov 0AkAk+1
for k = 1:(length(A)-1)
	pl = pl + 0.5*(A(1, k)*A(2, k+1) - A(2, k)*A(1, k+1));
end
%pristejemo se ploscino AnA1
pl = pl + 0.5*(A(1, k+1)*A(2, 1) - A(2, k+1)*A(1, 1));