Diference between subsamples

Once we have sorted and grouped all the samples and subsamples, we can create two matrices one that contains the odd samples (first subsample) and other with the even subsamples (second subsample), this way we can calculate the spectra difference between subsamples and check the spectra.

This difference spectra matrix is important to calculate the RMS between subsamples, that gave us an idea how similar are the subsamples between them. Just sum the squared values for every spectrum difference, divide by the number of wavelengths and calculate the square root.