SIMPSUM

If you want to integrate numerically an analytical function, you can use QUAD or similar. However, if you want to integrate already sampled data (equidistantly), and if the data are sufficiently smooth, instead of TRAPZ you will prefer SIMPSUM, numerical integration by Simpson method. It works on vectors and matrices (columnwise), calculates the average value of the sampled data, or simpson integral itself, if you supply the range(s) of independent variable(s). If you have nonequally spaced, but still smooth data, you can first resample them equidistantly with the help of some interpolation program like interp1(...'spline') and then apply SIMPSUM.