Heron's Formula and its Generalizations for the HP-41

Overview
 

 1°)  Area of a Triangle

  a)   Heron's Formula & Another one
  b)   M-Code Routines ( Heron & Brahmagupta Formulae )
  c)   Heronian Triangles

 2°)  Volume of a Tetrahedron

  a)   Francesca's Formula & Another one
  b)   2 M-Code Routines
  c)   6 Edges-lengths ---> 30 Volumes ?

 3°)  Hypervolume of a Simplex
 

Latest Updates:    programs in §1°)a) & 2°)a)

-In all these programs - except §1°-c) - we assume that all the edge lengths are known.
 

1°)  Area of a Triangle
 

     a)  Heron's Formula & Another one
 

-Let a triangle ABC with 3 known sides  a , b , c

-Heron's formula is     Area = [ p(p-a)(p-b)(p-c) ]^1/2      where  p = (a+b+c)/2 = semiperimeter
 

Data Registers: /
Flags: /
Subroutines: /

-Lines 08-09-10-11 may be replaced by the M-Code function  X/2
 
 

01 LBL "HERON"  02 ENTER  03 R^  04 ST+ Z  05 R^  06 ST+ T  07 R^  08 SIGN  09 ST+ X  10 ST/ L  11 X<> L  12 ST- Y  13 ST- Z  14 ST- T  15 *  16 *  17 *  18 CHS  19 SQRT  20 END

 
 ( 38 bytes / SIZE 000 )
 
 

STACK	INPUTS	OUTPUTS
Z	a	/
Y	b	/
X	c	Area

 
Example:      a = 2    b = 3    c = 4

   2   ENTER^
   3   ENTER^
   4   XEQ "HERON"  >>>>   Area = 2.904737510

Note:

-The formula may be re-written in a more stable one, that is given in reference [2]
-There will be less roundoff-errors in "difficult cases"
 
 

01  LBL "HERON"  02  STO T  03  X<>Y  04  STO M  05  ST+ T  06  X<> Z  07  ST+ Z  08  ST+ T  09  ST- M  10  RDN  11  ST- Y  12  ENTER^  13  X<> M  14  ST- Y  15  ST+ M  16  CLX  17  X<> M  18  *  19  *  20  *  21  SQRT  22  4  23  /  24  END

 
 ( 46 bytes / SIZE 000 )
 
 

STACK	INPUTS	OUTPUTS
Z	a	/
Y	b	/
X	c	Area

 
Example:      a = 2    b = 3    c = 4

   2   ENTER^
   3   ENTER^
   4   XEQ "HERON"  >>>>   Area = 2.904737510 

Note:

-The formula may also be re-written to have a smaller program:

    4 Area² = a² c² - ( a² + c² - b² )² / 4

01 LBL "ATR"  02 X^2  03 ENTER  04 R^  05 X^2  06 ST* Z  07 +  08 R^  09 X^2  10 -  11 2  12 /  13 X^2  14 -  15 SQRT  16 2  17 /  18 END

 
 ( 27 bytes / SIZE 000 )
 
 

STACK	INPUTS	OUTPUTS
Z	a	b
Y	b	b
X	c	Area

 
Example:      a = 2    b = 3    c = 4

   2   ENTER^
   3   ENTER^
   4   XEQ "ATR"  >>>>   Area = 2.904737510 

     b)  M-Code Routines ( Heron & Brahmagupta Formulae )
 

-"HERON" and "BRHM" use the Héron's & Brahmagupta's formulae.
-They are so similar that it is preferable to combine them.

-There is no check for alpha data and synthetic register Q is used.
-13-digit routines also give a better precision...
 

08E  "N"
00F  "O"
012  "R"
005  "E"
008  "H"
104   CLRF 8
033   JNC+06
08D  "M"
008   "H"
012   "R"
002   "B"
108   SETF 8
2A0  SETDEC
0F8  C=X
128   L=C
2BE  C=-C
10E  A=C ALL
0B8  C=Y
01D  C=
060   A+C
078   C=Z
025   C=
060   AB+C
04E   C=0 ALL
10C  ?FSET 8
01B   JNC+03
270   RAMSLCT
038   READATA
0E8   X=C
025   C=
060   AB+C
089   AB
064   STO Q+
0B8  C=Y
2BE  C=-C
10E   A=C ALL
138   C=L
01D  C=
060   A+C
078   C=Z
025   C=
060   AB+C
0F8   C=X
025   C=
060   AB+C
0D1  RCL
064   Q+
149   C=
060   AB*CM
089   AB
064   STO Q+
078   C=Z
2BE  C=-C
10E   A=C ALL
138   C=L
01D  C=
060   A+C
0F8   C=X
025   C=
060   AB+C
0B8  C=Y
025   C=
060   AB+C
0D1  RCL
064   Q+
149   C=
060   AB*CM
089   AB
064   STO Q+
0F8   C=X
2BE   C=-C
10E   A=C ALL
138   C=L
01D  C=
060   A+C
0B8  C=Y
025   C=
060   AB+C
078   C=Z
025   C=
060   AB+C
0D1  RCL
064   Q+
149   C=
060   AB*CM
04E   C
35C
050   =
190
226   16
269   C=
060   AB/C
305   C=
060   sqrt(AB)
0E8   X=C
3E0   RTN

( 96 words )
 
 

STACK	INPUTS	OUTPUTS
T	T	T
Z	a	a
Y	b	b
X	c	Area
L	/	c

 
Example1:      a = 2    b = 3    c = 4

   2   ENTER^
   3   ENTER^
   4   XEQ "HERON"  >>>>   Area = 2.904737510

Example2:     a = 4 , b = 5 , c = 6 , d = 7

   4  ENTER^
   5  ENTER^
   6  ENTER^
   7  XEQ "BRHM"  >>>>  Area = 28.98275349
 

     c)  Heronian Triangles
 

-The followig routine takes 3 integers in the stack and returns the integer edges lengths a , b , c  and area  A  of a Heronian triangle ( cf reference [3] ).
 

  Formula:

-With 3 integers  m , n , k  such that m.n > k²

   a = n ( m² + k² )
   b = ( m + n ) ( m.n - k² )           Area = A = k m n ( m + n ) ( m.n - k² )
   c = m ( n² + k² )
 

Data Registers:  R00 thru R03: temp
Flags: /
Subroutines: /
 
 

01  LBL "HETR"  02  STO 00   03  X^2  04  STO 03         05  X<>Y  06  STO 02

07  X^2  08  +  09  X<>Y  10  STO 01         11  ST* Y  12  RCL 02

13  ST+ Y  14  RCL 01         15  *  16  ST* 00  17  RCL 03  18  -

19  *  20  ST* 00  21  RCL 01         22  X^2  23  RCL 03  24  +

25  RCL 02  26  *  27  RCL 00         28  RDN  29  END

 
    ( 42 bytes / SIZE 000 )
 
 

STACK	INPUTS	OUTPUTS
T	/	Area
Z	m	c
Y	n	b
X	k	a

    With  m.n > k²

Example:      m = 67    n = 41    k = 13

   67   ENTER^
   41   ENTER^
   13   XEQ "HETR"   >>>>   a =  190978
                                  RDN    b =  278424
                                  RDN    c =  123950
                                  RDN   A =  9942799464

Note:

-"HETR" does not check that m.n > k² , so it may return ( meaningless ) negative results.
-Add for instance  X<0?  SF 99  after line 18.
 

2°)  Volume of a Tetrahedron
 

     a)  Francesca's Formula & Another one
 

-The volume of a tetrahedron may be calculated by the formula:

   V = [ 4 a² b² c² - a² ( b² + c² - d² )² - b² ( a² + c² - e² )² - c² ( a² + b² - f² )² + ( b² + c² - d² )( a² + c² - e² )( a² + b² - f² ) ]^1/2 / 12

 • • •  provided  the edges a , b , c intersect at the same vertex and  the edges d , e , f  are respectively opposite to the edges a , b , c

-So, a and d ( respectively b and e , c and f ) must be non-coplanar.
 
 
 

*                                      *      *                                   *             *                                *         d *     *                         c  *                           * e                          *                                 *                       *                         *              *                    *               b *               *          *                 *            *                              f *      *              *      *                                                *   *       V *   *   *   *   *   *   *   *   *   *   *   *   *   *   *                                          a

  

Data Registers:              R00: temp                                              ( Registers R01 thru R06 are to be initialized before executing "THV" )

                                      •  R01 = a       •  R04 = d
                                      •  R02 = b       •  R05 = e
                                      •  R03 = c       •  R06 =  f
Flags: /
Subroutines: /
 
 

01 LBL "THV"  02 RCL 03  03 X^2  04 4  05 RCL 02            06 X^2  07 STO 00  08 ST* Y  09 RCL 04

10 X^2  11 -  12 R^  13 ST* Z  14 +  15 STO Z  16 X^2  17 -  18 RCL 01

19 X^2  20 ST+ 00  21 ST* Y  22 R^  23 +  24 RCL 05            25 X^2  26 -  27 ST* Z

28 RCL 02  29 *  30 X^2  31 -  32 RCL 00            33 RCL 06  34 X^2  35 -  36 ST* Z

37 RCL 03            38 *  39 X^2  40 -  41 +  42 SQRT  43 12  44 /  45 END

 
    ( 61 bytes / SIZE 007 )

-Another program ( 60 bytes ) with the same formula:

Data Registers:              R00 & R07 temp                                           ( Registers R01 thru R06 are to be initialized before executing "THV" )

                                      •  R01 = a       •  R04 = d
                                      •  R02 = b       •  R05 = e
                                      •  R03 = c       •  R06 =  f
Flags: /
Subroutines: /
 
 

01 LBL "THV"  02 RCL 02  03 X^2  04 STO 00            05 RCL 03  06 X^2  07 STO 07  08 +  09 RCL 04

10 X^2  11 -  12 ENTER  13 X^2  14 RCL 00            15 RCL 07  16 *  17 4  18 *

19 -  20 RCL 01  21 X^2  22 ST+ 00  23 ST* Y  24 RCL 07            25 +  26 RCL 05  27 X^2

28 -  29 ST* Z  30 RCL 02            31 *  32 X^2  33 +  34 RCL 00  35 RCL 06  36 X^2  37 -

38 ST* Z  39 RCL 03            40 *  41 X^2  42 +  43 -  44 SQRT  45 12  46 /  47 END

 
    ( 60 bytes / SIZE 008 )

STACK	INPUT	OUTPUT
X	/	Volume

 
Example1:    a = 3   b = 5   c = 7   d = 6   e = 8   f = 4

-Store these 6 numbers into  R01 thru R06

  XEQ "THV"  >>>>   V = 8.426149775                        ---Execution time = 1.6s---

-The exact value is sqrt(71)

Example2:    a = 120   b = 160   c = 153   d = 25   e = 39   f = 56

-Store these 6 numbers into  R01 thru R06

  XEQ "THV"  >>>>   V = 8063.997493   whereas the exact result is 8064

-But if we store   39  56  120  160  153  25           into       R01  R02  R03  R04  R05  R06

  XEQ "THV"  >>>>   V = 8063.999990   much better precision !

Notes:

-The second tetrahedron is a heronian tetrahedron: the edges lengths, the faces areas & the volume are all integers.

-In difficult cases like example2, this formula may produce large roundoff-errors
-The method described in reference [2] is employed hereunder
 

 Data Registers:              R00-R07-R11: temp                                  ( Registers R01 thru R06 are to be initialized before executing "THV" )

                                      •  R01 = a       •  R04 = d
                                      •  R02 = b       •  R05 = e
                                      •  R03 = c       •  R06 =  f
Flags: /
Subroutines: /
 
 

01 LBL "THV"  02 RCL 02  03 RCL 03  04 +  05 STO 00  06 RCL 04  07 ST- 00  08 +  09 ST* 00  10 RCL 01  11 RCL 03  12 +  13 STO 07            14 RCL 05  15 ST- 07  16 +  17 ST* 07  18 RCL 01  19 RCL 02  20 +

21 STO 08  22 RCL 06  23 ST- 08  24 +  25 ST* 08  26 RCL 04  27 STO 09  28 RCL 02  29 RCL 03  30 -  31 ST- 09  32 +  33 ST* 09  34 RCL 05            35 STO 10  36 RCL 01  37 RCL 03  38 -  39 ST- 10  40 +

41 ST* 10  42 RCL 06  43 RCL 06  44 RCL 01  45 RCL 02  46 -  47 ST- Z  48 +  49 *  50 STO 11  51 RCL 10  52 RCL 09  53 *  54 *  55 SQRT  56 RCL 09            57 RCL 08  58 RCL 07  59 ST* 11  60 *

61 *  62 SQRT  63 RCL 08  64 RCL 00  65 ST* 11  66 *  67 RCL 10  68 *  69 SQRT  70 STO 09  71 R^  72 ST- 09  73 +  74 RCL X  75 RCL 11            76 SQRT  77 STO 11  78 R^  79 ST+ 11  80 -

81 ST- Z  82 +  83 *  84 RCL 11  85 RCL 11  86 RCL 09  87 ST- Z  88 +  89 *  90 *  91 SQRT  92 RCL 01  93 RCL 02            94 RCL 03  95 *  96 *  97 192  98 *  99 / 100 END

 
    ( 128 bytes / SIZE 012 )
 
 

STACK	INPUT	OUTPUT
X	/	Volume

 
Example:    a = 120   b = 160   c = 153   d = 25   e = 39   f = 56

-Store these 6 numbers into  R01 thru R06

  XEQ "THV"  >>>>   V = 8063.999986                                 ---Execution time = 3.4s---

Notes:

-It's not yet the exact result ( 8064 ), but the roundoff-errors are significantly smaller.

-We can also compute V  with   V = (1/3) Area x height


Data Registers:              R00-R07-R08-R09: temp                      ( Registers R01 thru R06 are to be initialized before executing "THV" )

                                      •  R01 = a       •  R04 = d
                                      •  R02 = b       •  R05 = e
                                      •  R03 = c       •  R06 =  f
Flags: /
Subroutines: /
 
 

01 LBL "THV"  02 RCL 05  03 X^2  04 RCL 04            05 X^2  06 -  07 STO Y  08 RCL 06  09 X^2  10 STO 08  11 ST+ Z  12 -

13 STO 00  14 RCL 02  15 X^2  16 RCL 01            17 X^2  18 STO 09  19 -  20 ST- 08  21 ST+ X  22 +  23 *  24 RCL 09

25 RCL 03  26 X^2  27 -  28 RCL 06            29 ST+ X  30 STO 07  31 ST/ 08  32 X^2  33 *  34 +  35 RCL 04  36 RCL 07

37 *  38 X^2  39 RCL 00            40 X^2  41 -  42 STO Z  43 SQRT  44 ST/ Y  45 +  46 RCL 07  47 ST+ X  48 /

49 X^2  50 CHS  51 RCL 09            52 +  53 RCL 08  54 X^2  55 -  56 *  57 SQRT  58 12  59 /  60 END

 
    ( 78 bytes / SIZE 010 )
 
 

STACK	INPUT	OUTPUT
X	/	Volume

 
Example:    a = 120   b = 160   c = 153   d = 25   e = 39   f = 56

-Store these 6 numbers into  R01 thru R06

  XEQ "THV"  >>>>   V = 8064     exact result !


-Another program with the formula:

   144 V² = a² b² ( d² + e² - f² ) + a² c² ( d² - e² + f² ) + b² c² ( -d² + e² + f² ) + a² d² ( -d² + e² + f² - a² ) + b² e² ( d² - e² + f² - b² ) + c² f² ( d² + e² - f² - c² ) - d² e² f²
 

Data Registers:              R00-R07-R08-R09-R10-R11-R12-R13-R14: temp                      ( Registers R01 thru R06 are to be initialized before executing "THV" )

                                      •  R01 = a       •  R04 = d
                                      •  R02 = b       •  R05 = e
                                      •  R03 = c       •  R06 =  f
Flags: /
Subroutines: /
 
 

01 LBL "THV"  02 RCL 04  03 X^2  04 STO 09  05 STO 12            06 RCL 06  07 X^2  08 STO 11  09 -  10 RCL 05  11 X^2  12 STO 10  13 ST- 12

14 +  15 STO 14  16 RCL 02  17 X^2  18 STO 07            19 *  20 RCL 12  21 RCL 11  22 ST- 12  23 +  24 STO 13  25 RCL 03  26 X^2

27 STO 08  28 ST- 14  29 *  30 +  31 RCL 12            32 RCL 01  33 X^2  34 STO 00  35 +  36 RCL 09  37 *  38 -  39 RCL 00

40 *  41 RCL 13  42 RCL 07            43 ST* 12  44 ST- Y  45 *  46 RCL 09  47 RCL 11  48 ST* 14  49 *  50 -  51 RCL 10

52 *  53 +  54 RCL 14  55 RCL 12            56 -  57 RCL 08  58 *  59 +  60 SQRT  61 12  62 /  63 END

 
    ( 78 bytes / SIZE 015 )
 
 

STACK	INPUT	OUTPUT
X	/	Volume

 
Example1:       a = 3   b = 5   c = 7   d = 6   e = 8   f = 4

-Store these 6 numbers into  R01 thru R06

  XEQ "THV"  >>>>   V = 8.426149775                        ---Execution time = 2.1s---

Example2:       a = 120   b = 160   c = 153   d = 25   e = 39   f = 56

-Store these 6 numbers into  R01 thru R06

  XEQ "THV"  >>>>   V = 8063.999990
 

     b)  2 M-Code Routines
 

-This program employs Francesca's formula with 13-digit routines
-The alpha "register" and registers Z , Y , L are cleared.

-The existence of data register R06 is checked but there is no check for alpha data.
-Register R00 is unused.
 

Data Registers:              R00: unused                             ( Registers R01 thru R06 are to be initialized before executing "THV" )

                                      •  R01 = a       •  R04 = d
                                      •  R02 = b       •  R05 = e
                                      •  R03 = c       •  R06 =  f
Flags: /
Subroutines: /
 

096  "V"
008  "H"
014  "T"
378  C=c
03C  RCR 3
226   C=C+1 S&X
106   A=C S&X
1BC  RCR 11
0A6  A<>C S&X
226  C=C+1 S&X
226  C=C+1 S&X
226  C=C+1 S&X
106   A=C S&X
1BC  RCR 11
0A6  A<>C S&X
226  C=C+1 S&X
226  C=C+1 S&X
070  N=C ALL
106  A=C S&X
130  LDI S&X
200  200h                         200h  is the correct value if you have an HP-41 CX, CV or C with a Quad memory module or 4 memory modules.
306  ?A<C S&X              If you have an HP-41C without any memory module, replace 200h by 100h
381  ?NCGO
00A  02E0                        if register R06  does not exist, the routine stops after displaying "NONEXISTENT"
0B0  C=N ALL
17C  RCR 6
270   RAMSLCT
038   READATA
10E  A=C ALL
0B0  C=N ALL
17C  RCR 6
226  C=C+1 S&X
270   RAMSLCT
038   READATA
2A0  SETDEC
135   C=
060   A*C
0B0   C=N ALL
03C   RCR 3
260   SETHEX
266  C=C-1 S&X
270   RAMSLCT
038   READATA
2A0  SETDEC
13D  C=
060   AB*C
04E  C
35C  =
090   2
13D  C=
060   AB*C
0AE  A<>C ALL
10E  A=C ALL
158   M=C ALL
0CE  C=B ALL
149   C=
060   AB*CM
081  0 ramslct
064  AB STO Q+
0B0  C=N ALL
17C  RCR 6
260  SETHEX
226  C=C+1 S&X
270   RAMSLCT
038   READATA
10E  A=C ALL
2A0  SETDEC
135   C=
060   A*C
046   C=0 S&X
270   RAMSLCT
0AE  A<>C ALL
128   L=C
0CE  C=B ALL
0E8  X=C
0B0  C=N ALL
03C  RCR 3
260  SETHEX
266  C=C-1 S&X
270   RAMSLCT
038   READATA
10E  A=C ALL
2A0  SETDEC
135  C=
060  A*C
046  C=0 S&X
270   RAMSLCT
138  C=L
158  M=C ALL
0F8  C=X
031  C=
060  AB+CM
0AE  A<>C ALL
128   L=C
0CE  C=B ALL
0E8  X=C
0B0  C=N ALL
03C  RCR 3
270   RAMSLCT
038   READATA
10E  A=C ALL
2BE  C=-C
135  C=
061  A*C
046  C=0 S&X
270   RAMSLCT
138  C=L
158  M=C ALL
0F8  C=X
031  C=
060  AB+CM
0AE  A<>C ALL
10E  A=C ALL
1A8  N=C
0CE  C=B ALL
168   M=C
0B0  C=N ALL
17C  RCR 6
270   RAMSLCT
038   READATA
13D  C=
060   AB*C
0AE  A<>C ALL
10E   A=C ALL
2BE  C=-C
158  M=C ALL
0CE  C=B ALL
149   C=
060   AB*CM
0C9  0 ramslct
064   RCL Q+
031  C=
060  AB+CM
089  AB
064  STO Q+
0B0  C=N ALL
17C  RCR 6
270   RAMSLCT
038   READATA
10E  A=C ALL
135   C=
060   A*C
046   C=0 S&X
270   RAMSLCT
0AE  A<>C ALL
128   L=C
0CE  C=B ALL
0E8  X=C
0B0  C=N ALL
03C  RCR 3
260  SETHEX
266  C=C-1 S&X
270   RAMSLCT
038   READATA
10E  A=C ALL
2A0  SETDEC
135  C=
060  A*C
046  C=0 S&X
270   RAMSLCT
138  C=L
158  M=C ALL
0F8  C=X
031  C=
060  AB+CM
0AE  A<>C ALL
128   L=C
0CE  C=B ALL
0E8  X=C
0B0  C=N ALL
260  SETHEX
266  C=C-1 S&X
270   RAMSLCT
038   READATA
10E  A=C ALL
2A0  SETDEC
2BE  C=-C
135  C=
061  A*C
046  C=0 S&X
270   RAMSLCT
138  C=L
158  M=C ALL
0F8  C=X
031  C=
060  AB+CM
0AE  A<>C ALL
10E  A=C ALL
228   P=C
0CE  C=B ALL
1E8   O=C
0B0  C=N ALL
17C  RCR 6
260  SETHEX
226  C=C+1 S&X
270   RAMSLCT
038   READATA
2A0  SETDEC
13D  C=
060   AB*C
0AE  A<>C ALL
10E   A=C ALL
2BE  C=-C
158  M=C ALL
0CE  C=B ALL
149   C=
060   AB*CM
0C9  0 ramslct
064   RCL Q+
031  C=
060  AB+CM
089  AB
064  STO Q+
0B0  C=N ALL
17C  RCR 6
270   RAMSLCT
038   READATA
10E  A=C ALL
135   C=
060   A*C
046   C=0 S&X
270   RAMSLCT
0AE  A<>C ALL
128   L=C
0CE  C=B ALL
0E8  X=C
0B0  C=N ALL
17C  RCR 6
260  SETHEX
226  C=C+1 S&X
270   RAMSLCT
038   READATA
10E  A=C ALL
2A0  SETDEC
135  C=
060  A*C
046  C=0 S&X
270   RAMSLCT
138  C=L
158  M=C ALL
0F8  C=X
031  C=
060  AB+CM
0AE  A<>C ALL
128   L=C
0CE  C=B ALL
0E8  X=C
0B0  C=N ALL
270   RAMSLCT
038   READATA
10E  A=C ALL
2BE  C=-C
135  C=
061  A*C
046  C=0 S&X
270   RAMSLCT
138  C=L
158  M=C ALL
0F8  C=X
031  C=
060  AB+CM
0AE  A<>C ALL
10E  A=C ALL
068   Z=C
0CE  C=B ALL
0A8  Y=C
0B0  C=N ALL
03C  RCR 3
260   SETHEX
266  C=C-1 S&X
270   RAMSLCT
038   READATA
2A0  SETDEC
13D  C=
060   AB*C
0AE  A<>C ALL
10E   A=C ALL
2BE  C=-C
158  M=C ALL
0CE  C=B ALL
149   C=
060   AB*CM
0C9  0 ramslct
064   RCL Q+
031  C=
060  AB+CM
089  AB
064  STO Q+
1B8  C=N
10E  A=C ALL
178  C=M
0EE  B<>C ALL
238  C=P
158  M=C ALL
1F8  C=O
149   C=
060   AB*CM
078  C=Z
158  M=C ALL
0B8  C=Y
149   C=
060   AB*CM
0D1  RCL
064  Q+
031  C=
060  AB+CM
04E  C=0 ALL
128  L=C
0A8  Y=C
068   Z=C
35C  C
050
110   =
110
226
226   144
269  C=
060  AB/C
305  C=
060  sqrt(AB)
0E8  X=C
345  ?NCGO
042  CLA

( 323 words )
 
 

STACK	INPUTS	OUTPUTS
T	T	T
Z	/	0
Y	/	0
X	/	Volume
L	/	0

        With   R01 = a  , ................. , R06 = f

Example1:    a = 3   b = 5   c = 7   d = 6   e = 8   f = 4

-Store these 6 numbers into  R01 thru R06

  XEQ "THV"  >>>>   V = 8.426149773

-The exact value is sqrt(71), so all the digits are correct.

Example2:    a = 120   b = 160   c = 153   d = 25   e = 39   f = 56

-Store these 6 numbers into  R01 thru R06

  XEQ "THV"  >>>>   V = 8063.999998
 

Notes:

-Register T is saved.
-With the second ( difficult ) example, even 13-digit routines don't give the exact result !

-Three steps are very similar in the calculations, so this routine may be simplified as follows ( 187 words instead of 323 ):

-Change the three ?NCXQ written in red according to the place of the subroutine in your own ROM
 

096  "V"                              @E143 in my ROM
008  "H"
014  "T"
378  C=c
03C  RCR 3
226   C=C+1 S&X
106   A=C S&X
1BC  RCR 11
0A6  A<>C S&X
226  C=C+1 S&X
106   A=C S&X
1BC  RCR 11
0A6  A<>C S&X
226  C=C+1 S&X
106   A=C S&X
1BC  RCR 11
0A6  A<>C S&X
226  C=C+1 S&X
070  N=C ALL                  CPU register N now contains the addresses of R01.R02.R03.R04
106  A=C S&X
130  LDI S&X
1FE  1FEh                         1FEh  is the correct value if you have an HP-41 CX, CV or C with a Quad memory module or 4 memory modules.
306  ?A<C S&X
381  ?NCGO
00A  02E0                         if register R06  does not exist, the routine stops after displaying "NONEXISTENT"
0B0  C=N ALL
27C  RCR 9
270   RAMSLCT
038   READATA
10E  A=C ALL
0B0  C=N ALL
17C  RCR 6
270   RAMSLCT
038   READATA
2A0  SETDEC
135   C=
060   A*C
0B0   C=N ALL
03C   RCR 3
270   RAMSLCT
038   READATA
13D  C=
060   AB*C
04E  C
35C  =
090   2
13D  C=
060   AB*C
0AE  A<>C ALL
10E  A=C ALL
158   M=C ALL
0CE  C=B ALL
149   C=
060   AB*CM
081  0 ramslct
064  AB STO Q+
04E  C=0 ALL
228   P=C
35C  C=
050   1
1E8  O=C
2A5  ?NCXQ        ?NCXQ                     Change these 2 words according to the address of the subroutine
384   E1A9             subroutine                  in your own ROM
260   SETHEX
0B0  C=N ALL
226   C=C+1 S&X
17C  RCR 6
266   C=C-1 S&X
23A  C=C+1 M
13C  RCR 8
070  N=C ALL
2A5  ?NCXQ        ?NCXQ                     Change these 2 words according to the address of the subroutine
384   E1A9             subroutine                  in your own ROM
260  SETHEX
0B0  C=N ALL
226  C=C+1 S&X
27A  C=C-1 M
17C  RCR 6
23A  C=C+1 M
13C  RCR 8
070  N=C ALL
2A5  ?NCXQ        ?NCXQ                     Change these 2 words according to the address of the subroutine
384   E1A9             subroutine                  in your own ROM
0D1  RCL
064  Q+
031  C=
060  AB+CM
04E  C=0 ALL
128  L=C
35C  C
050
110   =
110
226
226   144
269  C=
060  AB/C
305  C=
060  sqrt(AB)
0E8  X=C
345  ?NCGO
042  CLA
2A0  SETDEC          subroutine @E1A9 in my ROM
0B0  C=N ALL
17C  RCR 6
270   RAMSLCT
038   READATA
10E  A=C ALL
135   C=
060   A*C
046   C=0 S&X
270   RAMSLCT
0AE  A<>C ALL
1A8   N=C
0CE  C=B ALL
168  M=C
0B0  C=N ALL
270   RAMSLCT
038   READATA
10E  A=C ALL
2BE  C=-C
135  C=
061  A*C
046  C=0 S&X
270   RAMSLCT
1B8  C=N
158  M=C ALL
178  C=M
031  C=
060  AB+CM
0AE  A<>C ALL
1A8  N=C
0CE  C=B ALL
168  M=C
0B0  C=N ALL
03C  RCR 3
270   RAMSLCT
038   READATA
10E  A=C ALL
135  C=
060  A*C
046  C=0 S&X
270   RAMSLCT
1B8  C=N
158  M=C ALL
178  C=M
031  C=
060  AB+CM
0AE  A<>C ALL
10E  A=C ALL
0E8  X=C
0CE  C=B ALL
128   L=C
0B0  C=N ALL
27C  RCR 9
270   RAMSLCT
038   READATA
13D  C=
060   AB*C
0AE  A<>C ALL
10E   A=C ALL
2BE  C=-C
158  M=C ALL
0CE  C=B ALL
149   C=
060   AB*CM
0C9  0 ramslct
064   RCL Q+
031  C=
060  AB+CM
089  AB
064  STO Q+
238   C=P
10E  A=C ALL
1F8  C=O
0EE  B<>C ALL
0F8  C=X
158  M=C ALL
138  C=L
149  C=
060  AB*CM
0AE  A<>C ALL
10E  A=C ALL
228   P=C
0CE  C=B ALL
1E8  O=C
3E0  RTN                                    @E1FD in my ROM

( 187 words )
 
 

STACK	INPUTS	OUTPUTS
T	T	T
Z	Z	Z
Y	Y	Y
X	/	Volume
L	/	0

        With   R01 = a  , ................. , R06 = f

Notes:

-Same examples >>> same results.
-The alpha register is cleared but registers Y Z T are saved.
 

     c)  6 Edges Lenths ---> 30 Volumes ?
 

-Unlike the previous paragraphs, we assume that the sides d , e , f  intersect at the same vertex
  but  the sides d , e , f  are still respectively opposite to the sides a , b , c

-So, a and d ( respectively b and e , c and f ) must be non-coplanar.
 
 

*                                      *      *                                   *             *                                *         d *     *                         c  *                           * b                          *                                 *                       *                        *              *                    *               e *               *          *                 *            *                              f *      *              *      *                                                 *  *           *   *   *   *   *   *   *   *   *   *   *   *   *   *  *                                          a

 
-Given 6 values for the edges lengths, there are at most 30 different volumes for 30 tetrahedrons.
-The 30 volumes are stored into registers R40 to R11 and the corresponding configurations are:
 

     R40 =  a b c d e f    ( initial configuration )                R30 =  a b d c f e                  R20 = a c d b e f
     R39 =  a b c d f e                                                    R29 =  a b d c e f                  R19 = a c d b f e
     R38 =  a b c e f d                                                    R28 = a b f c e d                   R18 = a c e b f d
     R37 =  a b c f e d                                                    R27 = a b f e c d                   R17 = a b e c f d
     R36 =  a b c f d e                                                    R26 = a b f e c d                   R16 = a b e f c d
     R35 =  a b c e d f                                                    R25 = a b f d e c                   R15 = a b e f d c
     R34 =  a b d e c f                                                    R24 = a b f d c e                   R14 = a b e d f c
     R33 =  a b d e f c                                                    R23 = a b f c d e                   R13 = a b e d c f
     R32 =  a b d f e c                                                    R22 = a c f b d e                   R12 = a b e c d f
     R31 =  a b d f c e                                                    R21 = a c f b e d                   R11 = a c e b d f
 

 Data Registers:              R00 & R07 to R10 : temp                 ( Registers R01 thru R06 are to be initialized before executing "30THV" )

                                      •  R01 = a       •  R04 = d
                                      •  R02 = b       •  R05 = e                       R11 thru R40:  the 30 volumes corresponding to the 30 configurations above.
                                      •  R03 = c       •  R06 =  f
Flags: /
Subroutines: /
 
 

01  LBL "30THV"   02  4   03  STO 09    04  12   05  STO 10            06  41   07  STO 11   08  XEQ 01   09  RCL 05    10  X<> 06   11  STO 05   12  XEQ 01   13  RCL 04   14  X<> 06   15  STO 04   16  XEQ 01   17  RCL 04   18  X<> 05   19  STO 04   20  XEQ 01   21  RCL 05   22  X<> 06   23  STO 05   24  XEQ 01   25  RCL 04   26  X<> 06   27  STO 04   28  XEQ 01   29  RCL 03   30  X<> 05

31  STO 03   32  XEQ 01   33  RCL 05    34  X<> 06   35  STO 05            36  XEQ 01   37  RCL 04   38  X<> 05   39  STO 04    40  XEQ 01   41  RCL 05   42  X<> 06   43  STO 05   44  XEQ 01   45  RCL 04   46  X<> 05   47  STO 04   48  XEQ 01   49  RCL 05   50  X<> 06   51  STO 05   52  XEQ 01   53  RCL 03   54  X<> 06   55  STO 03   56  XEQ 01   57  RCL 04   58  X<> 05   59  STO 04   60  XEQ 01

61  RCL 05   62  X<> 06   63  STO 05    64  XEQ 01   65  RCL 04            66  X<> 05   67  STO 04   68  XEQ 01   69  RCL 05    70  X<> 06   71  STO 05   72  XEQ 01   73  RCL 04   74  X<> 05   75  STO 04   76  XEQ 01   77  RCL 02   78  X<> 04   79  STO 02   80  XEQ 01   81  RCL 05   82  X<> 06   83  STO 05   84  XEQ 01   85  RCL 03   86  X<> 06   87  STO 03   88  XEQ 01   89  RCL 05   90  X<> 06

91  STO 05   92  XEQ 01   93  RCL 03    94  X<> 06   95  STO 03            96  XEQ 01   97  RCL 02   98  X<> 04   99  STO 02  100  XEQ 01 101  RCL 04 102  X<> 05 103  STO 04 104  XEQ 01 105  RCL 05 106  X<> 06 107  STO 05 108  XEQ 01 109  RCL 04 110  X<> 05 111  STO 04 112  XEQ 01 113  RCL 05 114  X<> 06 115  STO 05 116  XEQ 01 117  RCL 04 118  X<> 05 119  STO 04 120  XEQ 01

121  RCL 02 122  X<> 04 123  STO 02  124  LBL 01 125  RCL 09          126  RCL 04 127  X^2 128  STO 07  129  ST* Y 130  RCL 03 131  X^2 132  - 133  RCL 05 134  X^2 135  STO 08 136  ST* Z 137  + 138  STO Z 139  X^2 140  - 141  RCL 06 142  X^2 143  STO 00 144  ST* Y 145  RCL 01 146  X^2 147  - 148  RCL 08 149  + 150  ST* Z

151  X^2 152  RCL 07          153  * 154  - 155  RCL 07  156  RCL 02 157  X^2 158  - 159  RCL 00 160  + 161  ST* Z 162  X^2 163  RCL 08 164  * 165  - 166  + 167  SIGN 168  LASTX 169  ABS 170  SQRT 171  * 172  RCL 10 173  / 174  DSE 11 175  STO IND 11 176  END

 
    ( 283 bytes / SIZE 041 )
 
 

STACK	INPUT	OUTPUT
X	/	V30 = R11

 
Example:     a = 41   b = 42  c = 43  d = 44  e = 45  f = 46

   41  STO 01      44  STO 04
   42  STO 02      45  STO 05
   43  STO 03      46  STO 06

   XEQ "30THV"   >>>>>   V₃₀ = 9549.651942 = R11                   ---Execution time = 65s---

-All the 30 volumes are

   R11 = 9549.651942     R16 = 9612.079808    R21 = 9572.860100    R26 = 9613.515867    R31 = 9613.268483    R36 = 9630.443600
   R12 = 9558.033600     R17 = 9599.960092    R22 = 9549.413017    R27 = 9592.100392    R32 = 9631.412675    R37 = 9634.972967
   R13 = 9560.585658     R18 = 9580.897258    R23 = 9557.078300    R28 = 9585.059600    R33 = 9626.096033    R38 = 9629.895233
   R14 = 9616.129400     R19 = 9581.612017    R24 = 9559.869292    R29 = 9587.918308    R34 = 9594.005417    R39 = 9621.832017
   R15 = 9625.694633     R20 = 9573.813792    R25 = 9609.267400    R30 = 9601.863525    R35 = 9619.220067    R40 = 9615.686350

Notes:

-The volume in R40 corresponds to the initial tetrahedron  41 - 42 - 43 - 44 - 45 - 46  ( a b c d e f )
-The volume in R11 corresponds to the tetrahedron  41 - 43 - 45 - 42 - 44 - 46  (  a c e b d f )

-Of course, all the configurations don't always lead to a real tetrahedron
-To avoid a data error if V² < 0 , "30THV" returns in fact  sign(V²) x sqrt ( abs ( V² ) )  Lines 167 to 173.
-So, the negative values must be read  sqrt(-1) | V |

-For instance, with  a = 6   b = 5  c = 2  d = 7  e = 8  f = 4  ,  R40 = 6 > 0  is a feasible tetrahedron
  but  R11 = -2 < 0 , R13 & R14 < 0 ... don't give real volumes.
-With these edges lengths, only 4 configurations lead to real volumes.

-The configurations "ACEBDF" .... could also be stored in registers to get more complete informations but it would cost many bytes...
-Another variant:

  Replace lines 174-175 by    X>0?   STOP    and delete lines 06-07

-Thus, the program will stop each time  V > 0  and you can recall R01 to R06 to get the corresponding config.

-If you prefer that the edges  a , b , c  intersect at the same vertex,  exchange R01<>R04 , R02<>R05 , R03<>R06  in the listing above.
 

3°)  Hypervolume of a Simplex
 

-We have to calculate a determinant of order ( n + 2 ) to get the (hyper-)volume of a n-simplex in a n-dimensional space.
-Let (n+1) points P_i  ( i = 1 , 2 , .... , n+1 )

    Let  B the matrix defined by  B_i,j = P_iP_j = distance between the 2 points
    and  C the matrix obtained if we add a top row  [ 0   1   1   .............  1 ]  and a left column [ 0   1   1   .............   1 ]^T  to matrix B
 

-The volume V of the simplex is then:    V = [ (-1)ⁿ⁺¹ 2 ^-n  det C ]^1/2 / n!
 

Data Registers:              The coefficients of the matrix C
                                         When the routine stops, R00 = det C and R01 = n

Flag:  F29
Subroutine:  "LS3"  or  "LS2"  or  "LS"  ( cf" Linear and non-linear systems for the HP-41" )
                                               or  "DET"  ( cf "Determinants for the HP-41" )

-The append character is denoted  ~
-Line 91 may be replaced by  XEQ "LCL"       ( cf "Miscellaneous Short Routines for the HP-41" )
-Line 100, n is saved in R01
 
 

01  LBL "SIMV"   02  STO 00   03  STO 01   04  5   05  +   06  STO 02    07  ST+ X   08  4   09  -   10  STO 03           11  CLX   12  FIX 0   13  CF 29   14  LBL 01   15  RCL 00    16  STO 06   17  RCL 02   18  STO 04   19  RCL 03   20  STO 05   21  R^   22  1

23  +   24  ENTER^   25  ISG X   26  LBL 02   27  " D"   28  ARCL Y   29  "~-"    30  ARCL X   31  "~?"    32  PROMPT   33  X^2   34  STO IND 04   35  STO IND 05   36  CLX   37  RCL 01           38  2   39  +   40  ST+ 05   41  SIGN   42  ST+ 04    43  +   44  DSE 06

45  GTO 02   46  RCL 01   47  3   48  +   49  ST+ 02   50  ST+ 03   51  R^   52  DSE 00   53  GTO 01   54  FIX 9   55  SF 29   56  RCL 01           57  2   58  +   59  STO 00    60  SIGN   61  LBL 03   62  STO IND L   63  DSE L   64  GTO 03   65  RCL 00   66  X^2

67  LASTX   68  -   69  1   70  +   71  RCL 00   72   E5   73  /   74  +   75  SIGN   76  LBL 04   77  STO IND L   78  DSE L   79  GTO 04   80  RCL 00           81  1   82  ST+ Y   83  %   84  RCL 00    85  X^2   86  +   87   E3   88  /

89  1   90  +   91  CLRGX   92  RCL 00    93  ENTER^   94  XEQ "LS3"   95  CHS   96  R^   97  INT   98  2   99  - 100  STO 01         101  LASTX 102  CHS 103  X<>Y 104  Y^X 105  / 106  SQRT 107  RCL 01  108  FACT 109  / 110  END

 
   ( 157 bytes / SIZE n²+4 n + 5 )
 
 

STACK	INPUT	OUTPUT
X	n > 1	Volume

 
Example1:   The tetrahedron of paragraph 2-a)

   Dim E = 3  XEQ "SIMV"  >>>    "D1-2?"

                        3      R/S      >>>    "D1-3?"
                        5      R/S      >>>    "D1-4?"
                        7      R/S      >>>    "D2-3?"
                        4      R/S      >>>    "D2-4?"
                        8      R/S      >>>    "D3-4?"
                        6      R/S      >>>    Volume = 8.426149767                           ---Execution time = 44s---

-The program is of course much slower: we have to calculate a determinant of order 5  instead of a relatively simple formula...
 

Example2:     In a 4-dimensional space, the simplex defined by 5 points  A , B , C , D , E  such that:

                      AB = 4  AC = 6  AD = 7  AE = 5
                      BC = 8  BD = 9  BE = 6
                      CD = 7  CE = 9
                      DE =10

    4  XEQ "SIMV"    >>>   "D1-2?"

           AB = 4  R/S   >>>   "D1-3?"
           AC = 6  R/S   >>>   "D1-4?"
           AD = 7  R/S   >>>   "D1-5?"
           AE = 5  R/S   >>>    "D2-3?"
           BC = 8  R/S   >>>    "D2-4?"
           BD = 9  R/S   >>>    "D2-5?"
           BE = 6  R/S   >>>     "D3-4?"
          CD = 7  R/S   >>>     "D3-5?"
          CE = 9  R/S   >>>     "D4-5?"
          DE =10 R/S   >>>     Volume = 27.22208051                              ---Execution time = 65s---

Note:

-If the distances are contradictory i-e if such a simplex cannot exist, there will be a DATA ERROR message line106
 

References:

[1]   http://mathworld.wolfram.com/Cayley-MengerDeterminant.html
[2]   Prof. W. Kahan - "What has the Volume of a Tetrahedron to do with Computer Programming Languages ?"
[3]   http://mathworld.wolfram.com/HeronianTriangle.html