function [A]=simps(x,y)

% Finds the area under a curve y(x) using Simpson's 2nd rule.
% x must have same step spacing, uneven length and be larger than
% equal to 3.
% /by Gloria Stenfelt Feb. 2015 @hib.no

n=length(x);
if mod(n,2)==0  || n<3
    disp('ERROR using simps: The length of vector x must be odd and at least 3.')
    A=nan;
    return
end

i=1:2:length(x)-2;
j=2:2:length(x)-2;
s424(i)=4;
s424(j)=2;

sf=[1 s424 1]; % Simpson factor vector

s=x(2)-x(1);

A=s/3 *  (sf*y');