I wrote, above: > The trajectory plot for a given flight doesn't seem to > appear on the lineprinter until the **succeeding** flight has > terminated. The visible trajectory plot always seems to be one > flight behind the one just terminated. I don't know what > that's about.
This turns out to be a subtle operational difference between using the SimH 1130 and a real machine. When the flight terminates, the console displays PLOT DIAGRAM IS READY. and the 1130 goes into a wait state (or SimH drops back to its command prompt), in response to a Fortran PAUSE statement in the main program. If you were using a real machine, this would be a chance to alter the data switches -- including, e.g., 5 = REJECT PLOT. in which case, when you continue, the plot data is **not** dumped to the lineprinter (though the headings for "TRACE EVERY TENTH ITERATION" are still printed, along with the trace data if switch #1 is on). But if switch #5 is off and you press PROGRAM START at that point, by the time ENTER ANGLE shows up on the console in preparation for the next flight, the plot diagram for the last flight is already coming out on the lineprinter. Which you can just walk over and see. But if you're using SimH, then this PAUSE (while also giving you a chance to alter data switches) is the **only** opportunity you'll get to view the lineprinter output (either by clicking the lineprinter icon in the GUI or by typing detach prt, view "printer.txt", !del printer.txt, attach prt printer.txt on the command line) without forcibly stopping the program (by clicking IMM STOP or by typing ^E in the console) after it has cycled around to display the next ENTER ANGLE prompt on the console. The location of the PAUSE statement in the main program comes immediately after "PLOT DIAGRAM IS READY." message is printed on the console, but **before** the plot data is actually written to the lineprinter. So if you do click the lineprinter icon in SimH when the program pauses after the message, you won't see the plot diagram for the flight that just ended, because it hasn't yet been sent to the lineprinter. And if you click the lineprinter icon after you've continued through the next flight and the program has once again paused after "PLOT DIAGRAM IS READY.", then you'll only see the plot diagram for the **previous** flight. I "fixed" this, just to make things more convenient for SimH, by commenting out the PAUSE statement on card LUNAR052 in the main program, and inserting a new PAUSE statement just after card LUNAR084 (immediately after the "DO 42" loop that writes the plot data out to the lineprinter). Of course, on a **real** 1130, this "fix" would make it impossible to avoid wasting time and paper if you decided you didn't need the plot for the just-completed flight. You can't have it both ways! BTW, if you enter angle "-135." and velocity increment "5000." the plot diagram shows that your ship loops once around the earth before heading off into space. It's also the case here that the program pauses twice **before** pausing for "PLOT DIAGRAM IS READY.". I was confused by this, but the instructions reveal what's going on: "THE PROGRAM WILL PAUSE WITH 2222 DISPLAYED WHEN THE 'X' COMPONENT OF VELOCITY APPROACHES ZERO..." That happens at the right and left extremities of the orbital loop. If you turn on tracing (switch #1), you can see the 'X' VELOC. changing sign and going through zero twice. And sure enough, when the program pauses, the Accumulator (in the GUI) shows __ __ _2 __ __ __ _6 __ __ __ 10 __ __ __ 14 __ 0 1 2 3 4 5 6 7 8 9 10 11 12 14 14 15 i.e., 0010 0010 0010 0010 2 2 2 2
