For modal dynamic calculations the response of the system is assumed to be a linear combination of the lowest eigenmodes. To this end, the eigenvalues and eigenmodes must have been calculated, either in the same run, or in a previous run. At the end of a frequency calculation this data, including the mass matrix, is stored in binary form in a .eig file. This file is read at the beginning of file dyna.c.
In file dynsolv.f the response is calculated in an explicit way, for details the reader is referred to [10]. Modal damping is allowed in the form of Rayleigh damping. Within file dynsolv the follwing routines are used: