Numerical codes to visualize topological phase transitions of nodal lines in a double diamond photonic crystal

<p><em>To observe nodal lines' phase transitions theoretically, the MIT Photonic Bands (MIT) and MATLAB codes are available. The codes in each folder calculate the band structures, eigenstates, and topological invariants and plot the figures in the paper. Each folder's name has the form of 'Fig2a', 'Fig3ab', etc., so that one can easily search the corresponding figures in the article. [Fig 2] If a band structure is calculated using an appropriate MPB code (not included here), the MATLAB codes in ‘Fig2’ shows the red and blue nodal lines using the gradient descent method. [Fig 3] The MPB codes in ‘Fig3’ calculate the eigenstates over the green rectangles shown in Fig 3a,c. Then, the MATLAB codes calculate the Euler forms, connections, and classes. [Fig 4] The MPB codes in ‘Fig4’ are to calculate the eigenstates along the paths Gamma-P_bar shown in Fig 4a-c. The MATLAB codes in the same folder then analyze the eigenstates to output the Zak phase. [Fig 6] All the subfolders in ‘Fig6’ contain the output band structure data by COMSOL Multiphysics. The MATLAB codes in the same folder display the output band structures shown in Fig 6d-i.</em></p>