Simultaneous equation solver for the HP-42S

This program is based on an RPL program written by Mike Ingle, originally posted on the HP Museum Forum.

To use the solver:

Enter your expressions and save them in variables. They should be expressions for which the calculator will find a zero. If you start out with equations, put parens around both sides and change the = to a - sign.

Enter initial guesses and save them in the appropriate variables. All the variables must exist, so the expressions will eval to numbers.

Enter four lines on the stack: List of expressions to solve. List of variables to solve for. Acceptable error, indicating when to stop. Delta (small number which is added to obtain slopes.)

Run the solver. If you saved it as MSLV, enter MSLV CLMF

Example: '2*X^3+Y+7*Z-96' 'E1' STO '3*X+6*Y^3-2*Z-65' 'E2' STO '-6*X+4*Y+2*Z^3-42' 'E3' STO 1 'X' STO 2 'Y' STO 3 'Z' STO { 'E1' 'E2' 'E3' } { 'X' 'Y' 'Z' } 1E-7 1E-7 MSLV CLMF

In 4 FIX: X=3.3161 Y=2.1666 Z=2.9857

After the first iteration, you will see two lines. The first shows the iteration count starting at 1. The second shows the worst residual. The first line will count up and the second will hopefully move toward zero.

If the equations are ill-behaved the program may generate an error. Try a different set of initial guesses.

The program evals each expression at the current guess and at guess + delta for each variable. It fills out a matrix of the slopes and a vector of the values, uses the built-in linear algebra to solve the linear system, subtracts the result from the guesses, and repeats until the worst residual is less than the acceptable error.

%%HP: T(3)A(R)F(.); \<< 4 PICK SIZE DUP IDN DUP2 SWAP 1 \->LIST RDM 0 DUP DO DROP 1 + 0 3 ROLL 1 6 PICK FOR i 9 PICK i GET DUP \->NUM 3 ROLL i 1 \->LIST 3 PICK PUT 3 ROLLD 1 8 PICK FOR j 10 PICK j GET 9 PICK DUP2 STO+ 8 ROLL i j 2 \->LIST 6 PICK \->NUM 6 PICK - 12 PICK / PUT 8 ROLLD STO- NEXT ABS 4 ROLL MAX 3 ROLLD DROP NEXT DUP 5 PICK / 1 7 PICK FOR i 9 PICK i GET OVER i 1 \->LIST GET STO- NEXT DROP 3 ROLLD OVER 1 DISP DUP 2 DISP UNTIL DUP 8 PICK < END 9 ROLLD 8 DROPN \>>

-- END --

Here's a quick-and-dirty port of Mike's program to the HP-42S. It could use some work to give it a nice user interface -- entering the vectors with the function and parameter names is pretty awkward right now. See the TEST program for how to initialize the parameters etc.; it's basically identical to Mike's RPL program.
In case you want to run it on an emulator, save yourself the trouble of typing and load ses.raw instead; it contains the Simultaneous Equation Solver. You may also want to get sestest.raw, which contains the three functions for the example given above, plus a test program that shows how to run the SES.

- Thomas

00 { 221-Byte Prgm } 01>LBL "SES" 02 CF 21 03 STO 00 04 Rv 05 STO 01 06 Rv 07 STO "VARS" 08 Rv 09 STO "EQS" 10 STO "RES" 11 DIM? 12 Rv 13 ENTER 14 ENTER 15 NEWMAT 16 STO "DER" 17 Rv 18 1E3 19 ÷ 20 1 21 + 22 STO 04 23 CLX 24 STO 02 25>LBL 00 26 1 27 STO+ 02 28 CLX 29 STO 03 30 RCL 04 31 STO 05 32>LBL 01 33 INDEX "EQS" 34 RCL 05 35 1 36 STOIJ 37 RCLEL 38 STO 07 39 INDEX "RES" 40 RCL 05 41 1 42 STOIJ 43 XEQ IND 07 44 STOEL 45 ABS 46 RCL 03 47 X<>Y 48 X>Y? 49 STO 03 50 RCL 04 51 STO 06 52>LBL 02 53 INDEX "VARS" 54 RCL 06 55 1 56 STOIJ 57 RCLEL 58 STO 08 59 RCL 00 60 STO+ IND 08 61 XEQ IND 07 62 RCL 00 63 STO- IND 08 64 INDEX "RES" 65 RCL 05 66 1 67 STOIJ 68 R^ 69 RCLEL 70 - 71 RCL÷ 00 72 INDEX "DER" 73 RCL 05 74 RCL 06 75 STOIJ 76 Rv 77 Rv 78 STOEL 79 ISG 06 80 GTO 02 81 ISG 05 82 GTO 01 83 RCL "DER" 84 STO÷ "RES" 85 RCL 04 86 STO 05 87>LBL 03 88 INDEX "RES" 89 RCL 05 90 1 91 STOIJ 92 RCLEL 93 INDEX "VARS" 94 RCL 05 95 1 96 STOIJ 97 RCLEL 98 R^ 99 STO- IND ST Y 100 ISG 05 101 GTO 03 102 CLA 103 RCL 02 104 AIP 105 |-"\LF" 106 ARCL 03 107 AVIEW 108 RCL 01 109 RCL 03 110 X>=Y? 111 GTO 00 112 CLD 113 END

00 { 37-Byte Prgm } 01>LBL "E1" 02 MVAR "X" 03 MVAR "Y" 04 MVAR "Z" 05 2 06 RCL "X" 07 3 08 Y^X 09 × 10 RCL+ "Y" 11 7 12 RCL× "Z" 13 + 14 96 15 - 16 END

00 { 40-Byte Prgm } 01>LBL "E2" 02 MVAR "X" 03 MVAR "Y" 04 MVAR "Z" 05 3 06 RCL× "X" 07 6 08 RCL "Y" 09 3 10 Y^X 11 × 12 + 13 2 14 RCL× "Z" 15 - 16 65 17 - 18 END

00 { 41-Byte Prgm } 01>LBL "E3" 02 MVAR "X" 03 MVAR "Y" 04 MVAR "Z" 05 -6 06 RCL× "X" 07 4 08 RCL× "Y" 09 + 10 2 11 RCL "Z" 12 3 13 Y^X 14 × 15 + 16 42 17 - 18 END

00 { 89-Byte Prgm } 01>LBL "TEST" 02 1 03 STO "X" 04 2 05 STO "Y" 06 3 07 STO "Z" 08 3 09 1 10 NEWMAT 11 ENTER 12 EDIT 13 "E1" 14 ASTO ST X 15 -> 16 "E2" 17 ASTO ST X 18 -> 19 "E3" 20 ASTO ST X 21 EXITALL 22 X<>Y 23 EDIT 24 "X" 25 ASTO ST X 26 -> 27 "Y" 28 ASTO ST X 29 -> 30 "Z" 31 ASTO ST X 32 EXITALL 33 1E-7 34 1E-7 35 XEQ "SES" 36 .END.