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### Modal dynamic calculations

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:

- tempload, to calculate the instantaneous loading
- rhs, to determine the external force vector of the system
- results, to calculate all displacements, stresses and/or any other variables selected by the user