Irvsp: to obtain irreducible representations of electronic states in the VASP

We present an open-source program "irvsp", to compute irreducible representations of electronic states for all 230 space groups with an interface to the Vienna ab-initio Simulation Package. This code is fed with plane-wave-based wave functions ($e.g.$ WAVECAR) and space group operators (listed in OUTCAR), which are generated by the VASP package. This program computes the traces of matrix presentations and determines the corresponding irreducible representations for all energy bands and all the $k$-points in the three-dimensional Brillouin zone. It also works with spin-orbit coupling (SOC), $i.e.$, for double groups. It is in particular useful to analyze energy bands, their connectivities, and band topology, after the establishment of the theory of topological quantum chemistry. In addition, the code has been also extended to (Wannier-based) tight-binding Hamiltonians. A sister program "ir2tb" is presented as well.