The **bounda_unknown** or **bounda_force** record with the same
*index* is imposed with the sum of the sine functions;
the first sine function has frequency *freq_0* and amplitude *amp_0*,
the second sine function has frequency *freq_1* and amplitude *amp_1*,
etc.. The sine functions starts at time 0.
More general behavior in time can be imposed by using **bounda_time**
records. For a specific *index* only one of **bounda_time** and
**bounda_sine** can be specified.

As a typical application the response due to the excitation
with a frequency spectrum can be analyzed.
Just print the relevant response by **control_print_history** and
extract the frequency spectrum of that response signal.

The sine loads will be only imposed after *start_time*.

tochnog 2001-09-02