I used compute_decomposition on a diagonal unitary matrix and the result is shown. I am curious to know on what mathematical principle compute_decomposition is constructed. I need more formulas to explain it.
Hi @RX1 , thanks for the question. 
You can find the explanation of how qml.DiagonalQubitUnitary.compute_decomposition works here, where there’s also the direct link to the source code. Hopefully this helps you along with the equations?
Alternatively, if you’re wondering about how to decompose your gate to a different gate set in PennyLane, you might want to check out this link: Compiling circuits — PennyLane 0.32.0 documentation