Creates a trajectory_t object with a prexisting underlying file named
  fn.  If fn does not exist, an error will be generated. If
  mode == 'rw', the file fn is opened for both reading and writing.
  If mode == 'r', the file fn is opened only for reading.
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| class(trajectory_t), | intent(out) | :: | this | |||
| character(len=*), | intent(in) | :: | fn | |||
| character(len=*), | intent(in) | :: | mode | |||
| integer, | intent(out) | :: | ierr |