**Babylonian doubling and halving algorithm for reciprocals , eTCL demo example calculator, numerical analysis**

This page is under development. Comments are welcome, but please load any comments in the comments section at the bottom of the page. Please include your wiki MONIKER  in your comment with the same courtesy that I will give you. Its very hard to reply intelligibly without some background of the correspondent. Thanks,[gold]
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[gold] Here is some eTCL starter  code for Babylonian doubling and halving algorithm for reciprocals  in calculator shell. For the Babylonian scribes, the standard table  gave reciprocals of regular numbers between 2 and 1_21 (decimal 81) as reciprocal pairs. There were a number of ways the reciprocals could be calculated, but the easiest way is called doubling and halving. An eTCL calculator was adapted to output the decimal equivalent of reciprocal pairs.with contraints,  mainly to study target number and factor selection on reciprocal algorithms. Additional console programs below are used to check or improve subroutine.

In the cuneiform math problems and coefficient lists on clay tablets, there are coefficient numbers which were used in determining the amount of materials and the daily work rates of the workers. In most cases, the math problem is how the coefficient was used in estimating materials, work rates, and math problems. One difficulty is determining the effective magnitude or power of the number coefficient in the base 60 notation. In cuneiform,  numbers in base 60 are written using a relative notation. For example, 20 could represent either 20*3600,20,20/60, 20/3600, or even 1/20. The basic dimensions and final tallies were presented in the cuneiform accounts on clay tablets, but some calculations and some units were left off the tablet. On the particular algorithms that use factoring, the relative value or uncertain magnitude makes a big difference because the factors of 20 and 1/20 are not the same.  At least one approach for the modern reader and using modern terminology is to develop the implied algebraic equations and decimal equivalents from the cuneiform numbers. Then the eTCL calculator can be run over a number of testcases to validate the algebraic equations. 


The doubling and halving algorithm for reciprocals was loaded into a console program below. Taking a known reciprocal pair of n and 1/n, the double target number has a (1/2)*reciprocal of the original in proportion. From modern notation, the new pair of reciprocals are 2*n and 1/(2*n).  Taking a known reciprocal pair of n and 1/n, the triple target number has a (1/3)*reciprocal of the original in proportion. Using modern notation, the new pair of reciprocals are 3*n and 1/(3*n). Generally, the notation is a*n and 1/(a*n), for a as a constant. The resulting reciprocals from  doubling and halving procedure in eTCL code seemed to work as a robust solution for positive integers, floating point numbers, and decimal fractions.
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         # take a known reciprocal pair of 2 and .5, set result from proportions
             set target_a 2.
             set reciprocal .5
             set doubling_halving_reciprocal [* [/ $target_a $target_number  ] $reciprocal  ]
======
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**Pseudocode Section**
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           # using pseudocode for Babylonian doubling and halving algorithm
           # for reciprocals 
           # irregular defined as not in standard B. table of reciprocals
       supplied values 
         lower limit
         upper limit
         start number
         factor
         standard table  N <  81
         1,2,4,8,16,32,64
         3,6,12,24,48
         5,10,20,40,80
         9,18,36,72 
        doubling and halving algorithm
        reciprocal pairs starting with 1
                                  1   1
                                  2   0.5
                                  4   0.25
                                  8   0.125 
       reciprocal pairs starting with 3                               
                                  3   0.333
                                  6   0.1666
                                 12   0.08333
                                 24   0.04166             
      Late Babylonian interest 1> N > 2
      need to compare result with TCL calculation
      check in error subroutine

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***Testcases Section***  

In planning any software, it is advisable to gather a number of testcases to check the results of the program. The math for the testcases can be checked by pasting statements in the TCL console. Aside from the TCL calculator display, when one presses the report button on the calculator, one will have console show access to the   capacity  functions (subroutines). 

**** Testcase 1 ****
%|table 1|printed in| tcl wiki format|% 
&| quantity| value| comment, if any|& 
&| 1:|testcase_number | |&
&| 1.0 :|lower limit  |   |&
&| 81.0 :|upper limit | |& 
&| 2.0 :|doubling factor (usually 2. ) | |& 
&| 0.5 :|optional: halving factor (usually 0.5 ): | |&
&| 4.0 :|answers: trial | |&
&| 1.0 :|function |  |&
&| 1.0 :|percentage error |  |&
&| 0.0 :|initial reciprocal |  |&
----

%|doubling_halving_algorithm|printed in| tcl wiki format| || |% 
&| quantity| value| factor |comment, if any|||&
&| line number | target number | factor |  reciprocal solution |||&
&| 1 | 2.0  | 0.5   | answer for reciprocal | 0.5  | 1/n comparison with tcl math |&   
&| 2 | 4.0  | 0.25   | answer for reciprocal | 0.25  | 1/n comparison with tcl math |&   
&| 3 | 8.0  | 0.125   | answer for reciprocal | 0.125  | 1/n comparison with tcl math |&   
&| 4 | 16.0  | 0.0625   | answer for reciprocal | 0.0625  | 1/n comparison with tcl math |&   
&| 5 | 32.0  | 0.03125   | answer for reciprocal | 0.03125  | 1/n comparison with tcl math |&   
&| 6 | 64.0  | 0.015625  | answer for reciprocal | 0.015625  | 1/n comparison with tcl math |&   
&| 7 | 128.0  | 0.0078125  | answer for reciprocal | 0.0078125  | 1/n comparison with tcl math |&   

**** Testcase 2 ****
**** Testcase 3 ****

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***Screenshots Section***
****figure 1.****
[Babylonian doubling and halving algorithm for reciprocals png]
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***References:***

   * Interpretation of reverse algorithms in several mesopotamian texts, Christine Proust
   * A Geometric Algorithm with Solutions to Quadratic Equations
   * in a Sumerian Juridical Document from Ur III Umma
   * Joran Friberg,  Chalmers University of Technology, Gothenburg, Sweden
   * google search engine <Trapezoid area bisection> 
   * Wikipedia search engine <Trapezoid area > 
   * mathworld.wolfram.com, Trapezoid and right trapezoid
   * Mathematical Treasure: Old Babylonian Area Calculation, uses ancient method
   * Frank J. Swetz , Pennsylvania State University
   * Wikipedia, see temple of Edfu, area method used as late as 200 BC in Egypt.
   * [Oneliner's Pie in the Sky] 
   * [One Liners] 
   * [Category Algorithm]
   * [Babylonian Number Series and eTCL demo example calculator]
   * [Brahmagupta Area of Cyclic Quadrilateral and eTCL demo example calculator]
   * [Gauss Approximate Number of Primes and eTCL demo example calculator]
   * Land surveying in ancient Mesopotamia, M. A. R. Cooper
   * [Sumerian Approximate Area Quadrilateral and eTCL Slot Calculator Demo Example , numerical analysis] 
   * Thomas G. Edwards, Using the Ancient Method of False Position to Find Solutions
   * Joy B. Easton, rule of double false position
   * Vera Sanford, rule of false position
   * www.britannica.com, topic, mathematics trapezoid
   * [Sumerian Equivalency Values, Ratios, and the Law of Proportions with Demo Example Calculator]
   * [Babylonian Sexagesimal Notation for Math on Clay Tablets in Console Example] 
   * Babylonians Tracked Jupiter With Advanced Tools: Trapezoids, Michael Greshko, news.nationalgeographic.com
   * Geometry in Babylonian Astronomy, Cluster of Excellence Topology, Humboldt University of Berlin
   * Mathieu Ossendrijver: „Ancient Babylonian astronomers calculated Jupiter’s position
   * from the area under a time-velocity graph“, in: Science, January 29, 2016.
   * Late Babylonian Field Plans in the British Museum, books.google.com/books 
   * Karen Rhea Nemet-Nejat
   * Late Babylonian Surface Mensuration Author(s): Marvin A. Powell Source: jstor
   * translation:  trapezoid in two babylonian astronomical cuneiform
   * texts for jupiter (act 813 & act 817) from the seleucid era , 310 BC -75 AD 
   * Otto Neugebauer, Astronomical Cuneiform Texts, 3 Vols. 
   * Lund Humphreys, London, 1955:405,430-31. 
   * DeSegnac, MS 3908 A RE-CONSTRUCTION,  D.A.R. DeSegnac
   * A draft for an essay 
   * DeSegnac, MENTAL COMPUTING OF THREE ARCHAIC
   * MESOPOTAMIAN PUZZLES W 20044, 35, W 20044, 20 & W 20214, essay draft
   * DeSegnac, HARMONY OF NUMBERS I and II,  D.A.R. DeSegnac, A draft for an essay
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**Appendix Code**

***appendix TCL programs and scripts ***
      
======
        # pretty print from autoindent and ased editor
        # Babylonian doubling and halving algorithm for reciprocals  calculator
        # written on Windows XP on eTCL
        # working under TCL version 8.5.6 and eTCL 1.0.1
        # gold on TCL WIKI, 2nov2017
        package require Tk
        package require math::numtheory
        namespace path {::tcl::mathop ::tcl::mathfunc math::numtheory }
        set tcl_precision 17
        frame .frame -relief flat -bg aquamarine4
        pack .frame -side top -fill y -anchor center
        set names {{} {lower limit :} }
        lappend names {upper limit:}
        lappend names {doubling factor (usually 2. ) : }
        lappend names {optional: halving factor (usually 0.5 ): }
        lappend names {answers: trial  :}
        lappend names {function : }
        lappend names {percentage error: }
        lappend names {initial reciprocal :} 
        foreach i {1 2 3 4 5 6 7 8} {
            label .frame.label$i -text [lindex $names $i] -anchor e
            entry .frame.entry$i -width 35 -textvariable side$i
            grid .frame.label$i .frame.entry$i -sticky ew -pady 2 -padx 1 }
        proc about {} {
            set msg "Calculator for doubling and halving algorithm for reciprocals
            from TCL WIKI,
            written on eTCL "
            tk_messageBox -title "About" -message $msg } 
       proc ::tcl::mathfunc::precision {precision float}  {
            #  tcl:wiki:Floating-point formatting, [AM]
            set x [ format "%#.5g" $float ]
            return $x
           }   
            #proc errorx always returns a positive error. 
            #Normally assume $aa is human estimate,
            #assume $bb is divinely exact.
       proc errorx  {aa bb} {expr { $aa > $bb ?   (($aa*1.)/$bb -1.)*100. : (($bb*1.)/$aa -1.)*100.}}
             proc doubling_halving_algorithm { target_number } {
             # initialize placeholder answer
             set doubling_halving_reciprocal 1.
             set target_a 2.
             set reciprocal .5
             set doubling_halving_reciprocal [* [/ $target_a $target_number  ] $reciprocal  ]
             return $doubling_halving_reciprocal
             }
       proc calculate {     } {
            global answer2
            global side1 side2 side3 side4 side5
            global side6 side7 side8 
            global lower_limit upper_limit doubling_factor
            global testcase_number
            global doubling_halving_reciprocal check_answer_product4
            incr testcase_number 
            set side1 [* $side1 1. ]
            set side2 [* $side2 1. ]
            set side3 [* $side3 1. ]
            set side4 [* $side4 1. ]
            set side5 [* $side5 1. ]
            set side6 [* $side6 1. ]
            set side7 [* $side7 1. ]
            set side8 [* $side8 1. ]
            # initialize placeholder answer
            set doubling_halving_reciprocal 1.
            set doubling_factor $side3
            # begin doubling_halving_algorithm
            set lower_limit $side1
            set upper_limit $side2
                    }
        proc fillup {aa bb cc dd ee ff gg hh} {
            .frame.entry1 insert 0 "$aa"
            .frame.entry2 insert 0 "$bb"
            .frame.entry3 insert 0 "$cc"
            .frame.entry4 insert 0 "$dd"
            .frame.entry5 insert 0 "$ee"
            .frame.entry6 insert 0 "$ff" 
            .frame.entry7 insert 0 "$gg"
            .frame.entry8 insert 0 "$hh" 
             }
        proc clearx {} {
            foreach i {1 2 3 4 5 6 7 8 } {
                .frame.entry$i delete 0 end } }
        proc reportx {} {
            global answer2
            global side1 side2 side3 side4 side5
            global side6 side7 side8 
            global lower_limit upper_limit doubling_factor
            global testcase_number
            console show;
            puts "%|table $testcase_number|printed in| tcl wiki format|% "
            puts "&| quantity| value| comment, if any|& "
            puts "&| $testcase_number:|testcase_number | |&"
            puts "&| $side1 :|lower limit  |   |&"
            puts "&| $side2 :|upper limit | |& "  
            puts "&| $side3 :|doubling factor (usually 2. ) | |& "
            puts "&| $side4 :|optional: halving factor (usually 0.5 ): | |&"
            puts "&| $side5 :|answers: trial | |&"
            puts "&| $side6 :|function |  |&"
            puts "&| $side7 :|percentage error |  |&"
            puts "&| $side8 :|initial reciprocal |  |&" 
            puts " reciprocal [ doubling_halving_algorithm 10 ] "
             set counter 1
             set keeper 1
             set reciprocal 1.
             puts "%|doubling_halving_algorithm|printed in| tcl wiki format| || |% "
             puts "&| quantity| value| factor |comment, if any|||&"
             puts "&| line number | target number | factor |  reciprocal solution |||&"
             set target_number 1.
             while { $keeper < $upper_limit  } {    
             set keeper [* $keeper $doubling_factor ] 
             set reciprocal [* $reciprocal [/ 1. $doubling_factor ] ] 
             puts "&| $counter | $keeper  | $reciprocal  | answer for reciprocal |
[/ 1. $keeper ]  | 1/n comparison with tcl math |&   "      
             incr counter   
             } 

            }
        frame .buttons -bg aquamarine4
        ::ttk::button .calculator -text "Solve" -command { set side8 0 ; calculate   }
        ::ttk::button .test2 -text "Testcase1" -command {clearx;fillup 1.  81.0 2.0 0.5  4.0   1.0   1.0    0.5}
        ::ttk::button .test3 -text "Testcase2" -command {clearx;fillup 1.0 81.0 2.0 0.5  9.0   1.0  0.138   2.1}
        ::ttk::button .test4 -text "Testcase3" -command {clearx;fillup 1.0 81.0 2.0 0.5  81.0  1.0  0.5     1.1}
        ::ttk::button .clearallx -text clear -command {clearx }
        ::ttk::button .about -text about -command {about}
        ::ttk::button .cons -text report -command { reportx }
        ::ttk::button .exit -text exit -command {exit}
        pack .calculator  -in .buttons -side top -padx 10 -pady 5
        pack  .clearallx .cons .about .exit .test4 .test3 .test2   -side bottom -in .buttons
        grid .frame .buttons -sticky ns -pady {0 10}
               . configure -background aquamarine4 -highlightcolor brown -relief raised -border 30
        wm title . "Babylonian Doubling and Halving Algorithm for Reciprocals Calculator"     
======
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*** Pushbutton Operation***

For the push buttons, the recommended procedure is push testcase and fill frame, change first three entries etc, push solve, and then push report. Report allows copy and paste from console. 

For  testcases in a computer session, the eTCL calculator increments a new testcase number internally, eg. TC(1), TC(2) , TC(3) , TC(N). The testcase number is internal to the calculator and will not be printed until the report button is pushed for the current result numbers. The current result numbers will be cleared on the next solve button.   The command { calculate; reportx  } or { calculate ; reportx; clearx  } can be added or changed to report automatically. Another wrinkle would be to print out the current text,  delimiters,  and numbers in a TCL wiki style table as

======
  puts " %| testcase $testcase_number | value| units |comment |%"
  puts " &| volume| $volume| cubic meters |based on length $side1 and width $side2   |&"  
======
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** Console program for doubling_halving reciprocal algorithm **
======
                  # autoindent from ased editor
                  # console program for doubling_halving reciprocal algorithm 
                  # written on Windows XP on eTCL
                  # working under TCL version 8.5.6 and eTCL 1.0.1
                  # TCL WIKI , 30jan2017
             console show
             package require math::numtheory
             namespace path {::tcl::mathop ::tcl::mathfunc math::numtheory } 
             proc doubling_halving_algorithm { target_number } {
             global side1 side2 side3 side4 side5
             global side6 side7 side8 
             global doubling_halving_reciprocal check_answer_product4
             # initialize placeholder answer
             set doubling_halving_reciprocal 1.
             set target_a 2.
             set reciprocal .5
             set doubling_halving_reciprocal [* [/ $target_a $target_number  ] $reciprocal  ]
             #puts "doubling_halving $doubling_halving_reciprocal "
             return $doubling_halving_reciprocal
             }
            # initialize placeholder answer
            set doubling_halving_reciprocal 1.
            # begin doubling_halving_algorithm
            # set doubling_halving_reciprocal [ doubling_halving_algorithm $target_number ]
             set counter 1
             puts "%|doubling_halving_algorithm|printed in| tcl wiki format| || |% "
             puts "&| quantity| value| factor |comment, if any|||&"
             puts "&| line number | target number | factor |  reciprocal solution |||&"
             set target_number 1.
             while { $counter < 50.  } {           
             set target_number [* 2. $target_number ]
             puts "&| $counter |$target_number  | [ doubling_halving_algorithm $target_number ] | answer for reciprocal |[/ 1. 

$target_number ] | 1/n comparison with tcl math |&   "      
             incr counter   
             } 
======
%|doubling_halving_algorithm|printed in| tcl wiki format| |1/n tcl math| |% 
&| quantity| value| factor |comment, if any|||&
&| line number | target number | factor |  reciprocal solution |||&
&| 1 |2.0  | 0.5 | answer for reciprocal |0.5 | comparison with tcl math |&   
&| 2 |4.0  | 0.25 | answer for reciprocal |0.25 | comparison with tcl math |&   
&| 3 |8.0  | 0.125 | answer for reciprocal |0.125 | comparison with tcl math |&   
&| 4 |16.0  | 0.0625 | answer for reciprocal |0.0625 | comparison with tcl math |&   
&| 5 |32.0  | 0.03125 | answer for reciprocal |0.03125 | comparison with tcl math |&   
&| 6 |64.0  | 0.015625 | answer for reciprocal |0.015625 | comparison with tcl math |&   
&| 7 |128.0  | 0.0078125 | answer for reciprocal |0.0078125 | comparison with tcl math |&   
&| 8 |256.0  | 0.00390625 | answer for reciprocal |0.00390625 | comparison with tcl math |&   
&| 9 |512.0  | 0.001953125 | answer for reciprocal |0.001953125 | comparison with tcl math |&   
&| 10 |1024.0  | 0.0009765625 | answer for reciprocal |0.0009765625 | comparison with tcl math |& 
----
%|doubling_halving_algorithm|printed in| tcl wiki format| |1/n tcl math| |% 
&| quantity| value| factor |comment, if any|||&
&| line number | target number | factor |  reciprocal solution |||&
&| 1 |0.02  | 50.0 | answer for reciprocal |50.0 | comparison with tcl math |&   
&| 2 |0.04  | 25.0 | answer for reciprocal |25.0 | comparison with tcl math |&   
&| 3 |0.08  | 12.5 | answer for reciprocal |12.5 | comparison with tcl math |&   
&| 4 |0.16  | 6.25 | answer for reciprocal |6.25 | comparison with tcl math |&   
&| 5 |0.32  | 3.125 | answer for reciprocal |3.125 | comparison with tcl math |&   
&| 6 |0.64  | 1.5625 | answer for reciprocal |1.5625 | comparison with tcl math |&   
&| 7 |1.28  | 0.78125 | answer for reciprocal |0.78125 | comparison with tcl math |&   
&| 8 |2.56  | 0.390625 | answer for reciprocal |0.390625 | comparison with tcl math |&   
&| 9 |5.12  | 0.1953125 | answer for reciprocal |0.1953125 | comparison with tcl math |&   
&| 10 |10.24  | 0.09765625 | answer for reciprocal |0.09765625 | comparison with tcl math |& 
----
%|tripling_taking 1/3 |printed in| tcl wiki format| |1/n tcl math| |% 
&| quantity| value| factor |comment, if any|||&
&| line number | target number | factor |  reciprocal solution |||&
&| 1 |3.0  | 0.3333333333333333 | answer for reciprocal |0.3333333333333333 | 1/n comparison with tcl math |&   
&| 2 |9.0  | 0.1111111111111111 | answer for reciprocal |0.1111111111111111 | 1/n comparison with tcl math |&   
&| 3 |27.0  | 0.037037037037037035 | answer for reciprocal |0.037037037037037035 | 1/n comparison with tcl math |&   
&| 4 |81.0  | 0.012345679012345678 | answer for reciprocal |0.012345679012345678 | 1/n comparison with tcl math |&   
&| 5 |243.0  | 0.00411522633744856 | answer for reciprocal |0.00411522633744856 | 1/n comparison with tcl math |&   
&| 6 |729.0  | 0.0013717421124828531 | answer for reciprocal |0.0013717421124828531 | 1/n comparison with tcl math |&   
&| 7 |2187.0  | 0.0004572473708276177 | answer for reciprocal |0.0004572473708276177 | 1/n comparison with tcl math |&   
&| 8 |6561.0  | 0.00015241579027587258 | answer for reciprocal |0.00015241579027587258 | 1/n comparison with tcl math |&   
&| 9 |19683.0  | 5.080526342529086e-5 | answer for reciprocal |5.080526342529086e-5 | 1/n comparison with tcl math |&   
&| 10 |59049.0  | 1.6935087808430286e-5 | answer for reciprocal |1.6935087808430286e-5 | 1/n comparison with tcl math |&   

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[gold] This page is copyrighted under the TCL/TK license terms, [http://tcl.tk/software/tcltk/license.html%|%this license]. 

**Comments Section**

<<discussion>>
Please place any comments here, Thanks.

                              
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