This is answered in this reddit post: www.reddit.com/r/fea/comments/1covgq3/how_do_you_output_the_stiffness_matrix_to_the_h5/? Below I quoted some of the answer. Solution: Add this case control command. EXTSEOUT(extid=100,hdf5) This generates an H5 file, e.g. dsoug1.odys.h5, with stiffness matrix KAA. Refer to figure 1. EXTSEOUT only works with MSC Nastran. This will NOT work with other Nastran types, e.g. NX Nastran, NEi Nastran, etc. PARAM,EXTOUT,DMIGPCH was also used to confirm the stiffness matrix in the PCH file also matches the matrix in the H5 file. EXTSEOUT and PARAM,EXTOUT,DMIGPCH do not work together, so use these entries separately. This was done with MSC Nastran 2023.3. Note that this may or may not be compatible with older and future versions of MSC Nastran. If you see this post in the year 2030, EXTSEOUT may no longer be available. Tools Used: MSC Nastran 2023.3 on Linux. Notepad++ - notepad-plus-plus.org/ HDFView - Registration is required, but free to download: www.hdfgroup.org/downloads/
