Encyclopaedia Index


SATELLITE is the pre-processing program of the PHOENICS suite.

(1) What SATELLITE does

SATELLITE prepares the input data for the simulation.

It also provides access to:-

Typing 'runsat' at the operating-system prompt activates it.

SATELLITE is an interpreter; from instructions provided by the user it creates a data file called EARDAT, and for BFC problems another called XYZ, containing instructions which EARTH can understand and obey.

SATELLITE may receive its instructions from the user in several ways, including:

SATELLITE also possesses a FORTRAN subroutine called SATLIT into which data-setting statements can be inserted by the user, and another called MAIN which permits DIMENSION changes to be made. Re-compilation of SATLIT and re-linking of SATELLITE are necessary before such changes become effective.

(2) How SATELLITE works

Information is processed by SATELLITE in the following order:

  1. The default values of all data items are set.
  2. The pre-existing Q1 file is read.
  3. The subroutine SATLIT is executed.
  4. The program interacts with the user, if TALK=T, by way of the VDU and keyboard.
  5. The data inputs, supplied by the user during the 'TALK' session and recorded on the COPYQ1 file, are transferred to the Q1 file if the user answers Y , when asked.
  6. A suitably-processed version of the data is written to the file called EARDAT for transmission to EARTH.

The following brief notes about each item supplement what has been written above.

(a) The default settings

The default settings of the PHOENICS variables are set by a subroutine which is not accessible to the user; they are therefore always the same.

What the values are can be observed, in part, by the use of the SEE command, when an empty Q1 is interpreted.

However, values pertaining to particular dependent variables are disclosed by SEE only if the instruction has already been given to solve for those variables.

It is necessary at least to give positive SOLVE instructions if the default values are to be SEEn.

(b) The Q1 file

Examples of Q1 files are provided in the PHOENICS Input Library. (See also PHENC: Q1)

SATELLITE always begins by reading the first line of the Q1 file, in order to learn whether the conversational mode is to be used, and how many distinct runs are in question.

RUN(1,1) indicates that only one run is to be performed; whereas RUN(10,15), for example, would dictate the performance of runs 10 to 15 inclusive.

The built-in interpreter of the SATELLITE then reads through all subsequent lines until it encounters the STOP instruction.


Having read Q1, the SATELLITE program executes the FORTRAN subroutine SATLIT, into which the user is allowed, if he wishes, to insert his own FORTRAN coding sequences. As PIL has become more powerful, so the need for such insertions has become less, so that nowadays SATLIT is rarely modified. (See PHENC: SATLIT)

(d) Interactive use

When the PHOENICS SATELLITE is activated in the TALK=T mode, the user is presented with an invitation to set input-data items; but this may be declined by typing END at once whereupon PHOENICS will work with the 'default' values of all its variables, except insofar as these were modified by the instructions contained in Q1 and (if any) in SATLIT.

If he does accept the invitation, the user can proceed via menu and mouse or via the keyboard.

The types of command which can be entered directly at the keyboard or indirectly via mewnu and mouse fall into six categories, viz:

  1. variable-setting commands;
  2. argument-setting commands;
  3. termination commands;
  4. data-display commands;
  5. information-seeking commands; and

Details of each of these categories are supplied in the PHOENICS Encyclopaedia entry: PIL.

(e) The COPYQ1 file

All syntactically-valid data-setting commands and comments (ie command categories 1,2 and 6), read from the Q1 file or supplied during the interactive session, are written to the file COPYQ1. Thus, if the computer system 'crashes' during a 'TALK' session, the entries already made are not lost.

(f) The file EARDAT

SATELLITE 'speaks' to EARTH by means of the file named EARDAT. The user need to know this only so that he can interpret error messages which appear, for example, when an attempt is made to run EARTH before SATELLITE has been run; for then a reference to logical unit 10 and/or the absence of EARDAT is likely to appear on the VDU.