TI-57 Lunar Lander ?

[pauln]

I have been looking for a Lunar Lander for TI-57/RCL-57 and I came across this older thread. I ended up writing my own version which I list here for anyone interested.

IMO, it has a few advantages over the one in "L'Ordinateur de Poche":

• It displays the sign of the velocity, making clear whether the rocket is descending or not
• There is no need to enter the fix mode
• It gives a clear indication that the game has ended (display blinking)
• It computes velocity and altitude every second, looking for landing or a crash, instead of doing so only every 10 seconds
  

Instructions:

1. Key in the program
2. Enter initial velocity: 100 STO 1
3. Enter initial altitude: 2500 STO 2
4. Enter initial fuel: 100 STO 3
5. RST R/S
   You should see "100" (fuel) followed by "100.2500" (velocity.altitude).
6. 'N' R/S
   where 'N' (N integer >= 0) is the number of gallons to consume in the next 4 seconds.
   You should see "fuel" and, after a pause, "velocity.altitude"
7. Repeat Step 6 until the display blinks
   if >= 0, you landed safely
   if < 0, you crashed
   

If you want to see your final velocity, press RCL 1.

Code:


# Displays the current state.
RCL 3 INV Fix Pause                    # Fuel 
RCL 1 x:t 1 +/- INV x>=t +/-           # Compute sign of velocity
x
RCL 2 / 4 INV log + RCL 1 = Fix 4      # velocity.altitude
R/S

# Updates the fuel available
STO 4                                  # Number of gallons for the next 4 seconds
x:t RCL 3 INV x>=t STO 4               # Ensure it doesn't exceed quantity of fuel left
RCL 4 INV SUM 3                        # Update fuel

# Loops 4 times (4 seconds)
5 STO 0 Lbl 0 INV Dsz RST

# Updates the altitude and velocity after 1 second
RCL 1 INV SUM 2                        # Altitude
5 SUM 1 RCL 4 INV SUM 1                # Velocity

# Determines what happened in the last second
RCL 2 C.t INV x>=t GTO 7               # Crash: note the non existent label 7
6 x:t
RCL 1 |x| + RCL 2 = x>=t GTO 0         # Not landing: loop back

# Safe landing: if |velocity| + altitude <= 5, the display will blink (>= 0) since GTO 0 is at the last step (49)

[Thomas Klemm]

(06-04-2022 06:22 PM)pauln Wrote:  

Code:

# Loops 4 times (4 seconds)
5 STO 0 Lbl 0 INV Dsz RST

I was not sure whether to trust the comment or the code.
Therefore I changed it to:

Code:

# Loops 4 times (4 seconds)
4 STO 0 Lbl 0 INV Dsz RST

With this I came up with the following solution to a safe landing:

100.
100.2500

5 R/S

95.
100.2200

5 R/S

90.
100.1900

5 R/S

85.
100.1600

5 R/S

80.
100.1300

5 R/S

75.
100.1000

10 R/S

65.
85.0715

10 R/S

55.
70.0475

10 R/S

45.
55.0280

10 R/S

35.
40.0130

10 R/S

25.
25.0025

25 R/S

»5.0000«

That was surprisingly fun to figure out.

---

Here's a mostly verbatim translation of the program for the HP-42S:

Code:

00 { 92-Byte Prgm }
01▸LBL "LUNAR"
02 2500
03 STO 02
04 100
05 STO 01
06 STO 03
07▸LBL 01
08 "Fuel: "
09 ARCL 03
10 ├" Vel: "
11 ARCL 01
12 ├"[LF]Alt: "
13 ARCL 02
14 PROMPT
15 RCL 03
16 X>Y?
17 X<>Y
18 STO 04
19 STO- 03
20 4
21 STO 00
22▸LBL 00
23 DSE 00
24 FS? 00 # assume it is clear
25 GTO 01
26 RCL 01
27 STO- 02
28 5
29 STO+ 01
30 RCL 04
31 STO- 01
32 RCL 02
33 X<0?
34 GTO 07
35 6
36 RCL 01
37 ABS
38 RCL 02
39 +
40 X≥Y?
41 GTO 00
42 END

[Thomas Klemm]

(06-12-2022 07:00 PM)Thomas Klemm Wrote:  I was not sure whether to trust the comment or the code.

Well, I should have read this code more thoroughly.
There's no reason to change it.

[pauln]

Nice!

As you noticed later, by changing the value from 5 to 4, you are only descending for 3 seconds. On the other hand, with that change, the game becomes quite a bit harder and arguably more interesting for the experienced Lunar Lander player.