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Full Version: (50G) Lambert w function for reals

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For real number input the programme LAMBW returns the value of the Lambert w function to the stack.

For info on the function see

http://mathworld.wolfram.com/LambertW-Function.html

Code:

::

  CK1&Dispatch

  BINT1

  ::

    '

    ID 0

    TRUE

    3PICK3PICK

    DUP'

    %EXP

    '

    %*

    '

    %-

    BINT6

    SYMBN

    3PICK

    5PICK

    DUP

    % 500.

    %<=

    ITE

    ::

      %1+

      %LN

      DUP

      % .0195

      %*

      %1+

      %*

      % .665

      %*

      % .04

      %+

    ;

    ::

      DUP

      %4

      %-

      %LN

      SWAP

      %LN

      %1

      OVER

      %1/

      %-

      SWAP

      %LN

      %*

      %-

    ;

    NUMSOLVE

    2DROP

    SWAP

    ?PURGE_HERE

    SWAP

    xDROP

  ;

;

Reference URL's

HP Forums: https://www.hpmuseum.org/forum/index.php
:

HP Forums

Gerald H