where 𝑦 𝑖 is the total count at m/z bin 𝑖, 𝑥 𝑗 is the abundance of cluster 𝑗, and 𝑎 𝑖𝑗 is the relative intensity of the 𝑖 𝑡ℎ isotope in the isotopic distribution of the 𝑗 𝑡ℎ cluster. In matrix form, this entire relationship for the observed spectra can be written: