Encyclopaedia Index

INTRODUCTION TO PIL

Contents

• Further Details On The Q1 File
• Getting Help And Status Checking
• Access To The Library
• Ending The Session
• The SATELLITE Stack
• The PIL Tutorials
• The Encyclopaedia entry on PIL

Further Details On The Q1 File

• Data settings in Q1 are arranged into Groups. There are 24 Groups, the titles of which are frequently inserted as comments. An empty Q1 with the Group names would be:

TALK=T;RUN(1,1)

GROUP 1. Run title and other preliminaries

GROUP 2. Transience; time-step specification

GROUP 3. X-direction grid specification

GROUP 4. Y-direction grid specification

GROUP 5. Z-direction grid specification

GROUP 6. Body-fitted coordinates or grid distortion

GROUP 7. Variables stored, solved & named

GROUP 8. Terms (in differential equations) & devices

GROUP 9. Properties of the medium (or media)

GROUP 10. Inter-phase-transfer processes and properties

GROUP 11. Initialization of variable or porosity fields

GROUP 12. Convection and diffusion adjustments

GROUP 13. Boundary conditions and special sources

GROUP 14. Downstream pressure for PARAB=.TRUE.

GROUP 15. Termination of sweeps

GROUP 16. Termination of iterations

GROUP 17. Under-relaxation devices

GROUP 18. Limits on variables or increments to them

GROUP 19. Data communicated by satellite to GROUND

GROUP 20. Preliminary print-out

GROUP 21. Print-out of variables

GROUP 22. Spot-value print-out

GROUP 23. Field print-out and plot control

GROUP 24. Dumps for restarts

STOP

• The group list is just an aide-memoire, and not a questionnaire that has to be filled in.
• Not all the groups must be provided with data settings, for all PIL variables have default values; PIL commands do not need to be placed in the Group they 'belong' to; and, furthermore, the Group list itself is just a reminder and does not need to be present at all.
• PIL is an interpreted language (like most BASIC), not a compiled language (like FORTRAN). Each statement is implemented immediately it is read in, either from Q1 or from the keyboard.
• Statements starting in column 3 or greater are treated as comments.

Getting Help And Status Checking

• Entering '?' will elicit general advice, and suggestions for further inquiry.
• Entering a variable or command followed by '?' will elicit help on that item. All on-line help entries are also printed in the PHOENICS Reference manual, TR/200a and are available through the on-line Encyclopedia.
• Entering a variable followed by RETURN will cause Satellite to display the current setting of that variable.
• The command SEE will cause Satellite to display all currently active variables in Group 1. Further RETURNs will display subsequent Groups.
• SEE n will display the settings in Group n directly.
• GROUPn will display a list of all variables and commands 'belonging' to group n.

Access To The Library

• The command SEELIB will display the contents of the PHOENICS Input Library, starting with the contents list.
• Cases from the Input Library can be accessed by LOADing them:

LOAD(case_number)

• Further commands or menu settings will then act to modify the basic Library case.

Ending The Session

• Once all data settings have been made and are correct, the command END will cause Satellite to write out the EARDAT file for Earth and stop.
• Before stopping, the user is given the opportunity to overwrite the existing Q1 file with the 'stack' of commands held in the Satellite memory.
• This will contain all that was read in from Q1 together with all that has been entered at the keyboard.
• If the user answers NO to the 'overwrite Q1?' question, and only then realises that three hours of hard work have been lost, they should not despair. The file COPYQ1 will contain a copy all this material until the next time Satellite is executed.

The Satellite Stack

• Previous panels have mentioned that PIL is interpreted as soon as it is read. All legal commands are held in a 'stack', which can be inspected - and changed - by the user. EDITOR? will elicit information on how the stack editor works.
• The stack editor is needed because of the interpretive nature of PIL. The commands GRDPWR(X,5,1,1); CONPOR(BL1,0,CELL,1,NX... will set NX (Number of cells in X) to 5, and then the X limits of the CONPOR to 1,5. A subsequent NX=10 will change NX, but NOT the grid or the CONPOR limits. The stack editor can be used to make the change in the right place.
• Once the stack has been edited, LOAD(STACK) will cause the new sequence of commands to be interpreted immediately. This would happen by default if END were entered without a LOAD(STACK).

The Pil Tutorials

• Three PIL-language tutorials have been provided in the form of the Input-Library cases numbered 091, 092 and 093.
• Each one guides you through a complete problem setup, which you can then run through Earth, and visualise with Photon.
• For beginners, a simple way to run a tutorials is to create a Q1 file containing the three lines (for the first case):

  
          TALK=F;RUN(1,1)
          LOAD(091)
          STOP
           and then to issue at the DOS prompt the command:     

  
          RUNSAT
       

• Messages appearing on the screen will then provide instructions and advice.
• Inspection of the files 091.htm, 092.htm and 093.htm, to be found in \phoenics\d_earth\d_core\inplib\, will reveal that these files are themselves written in PIL, which provides all the necessary interactive features.
• An effective way of studying these features is to run the satellite code in one window and the browser in another; the former will see the effects of which the latter will reveal the causes.