Specfem3D and Full Waveform Inversion# Rules of meshes in Specfem3D Define coordinates Set elements and materials Avoid numerical dispersion Receiver Function Forward simulation with Specfem3D_FWATR Preparation Run simulation Add velocity perturbation Add velocity perturbation onto gll data format file Virtualization of GLL data format measure_adj: A software package for making measurements and computing adjoint sources for seismic tomography Introduction Getting started Obtaining the code Compilation Running MEAS–ADJ Measurement options More Notes Miscellaneous Notes and Acknowledgments Gallery Reference How to determine an optimal step length Armijo rule and curvature