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SIMION 8.0 Issues/Bugs/Enhancements

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Issue I353 [80,prog,change,resolved]
  Change in behavior of adjustable variable assignments in
    Lua affecting current v.s. default values.
  Suggested by davidm-20070118 to improve ion trap example.

  As of 8.0.2, the behavior of when assignments to adjustable
  variables in Lua affect current v.s. default values was changed
  slightly to be more reasonable.  A quick executive summary is
  given first followed by the full excruciating details.

  Summary...

  This change is somewhat subtle and has no effect on most programs
  that simply define adjustable variables and use them in segments,
  but some programs that do more complicated things with adjustable
  variables can be affected (e.g. the "trap" example that redefines
  some adjustable variables from one Lua file in another Lua file),
  particularly when the user adjusts these variables from the
  Variables tab in View.  Under the old behavior, adjustments made to
  these variables in the Variables tab in View could get ignored
  (i.e. the program, in overriding these variables, also overrides the
  user).  Under the new behavior, the user adjustments are not
  ignored.

  Namely, under the new behavior, assignments to an adjustable
  variable from Lua programs ALWAYS affect the current value and not
  the default value.  Moreover, following program loading (and before
  the Fly'm), the current values are used to define the default
  values.

  Discussion...

  Each SIMION adjustable variable has both a "current value" and a
  "default value".  The default value is defined in the
  program.  It typically doesn't change, but it will be reset if
  changed in the user program source code that is then reloaded, as
  occurs on (re)loading the workbench and also starting a new Fly'm.
  The current value is initially set to the default value.  The user
  or the program can change the current value at run-time.  The
  current value is reset to the default value if you click "Reset
  Values" on the Variables tab.  SIMION also saves and restores the
  current value before and after a Fly'm so that the current value
  after a Fly'm is the current value before a Fly'm.

  In SIMION 8.0.0-8.0.1, the statement

    adjustable x = 3

  when executed sets the default value for the adjustable variable x
  to 3.  It leaves the current value unchanged except when the default
  value changes, in which case the current value is reset to the
  default value. In contrast, the following seemingly similar code has
  a different behavior:

    adjustable x
    x = 3

  The first line does not change the current/default values but the
  second line updates the current value.  Note that only "adjustable"
  assignment statements (which act as declarations) touch the default
  value.

  Typical usage is this:

    simion.workbench_program()
    adjustable x = 3   -- define default value
    function segment.other_actions()
      print(x)
      x = x + 1   -- update current value temporarily in Fly'm.
    end

  When the program is loaded, the default value becomes 3.  The
  current value is normally unchanged at that time, but it will reset
  to the default value if the default value changes (as might occur if
  you change the value in the second line of the program and then
  reload the program such as by reloading the workbench or starting a
  new Fly'm).  Later, when the other_actions segment runs during the
  Fly'm, the current value of x is updated.  Changes to the current
  value remain in effect until the Fly'm finishes, in which case the
  current value of x is reset to its current value before the Fly'm.

  The change in behavior in 8.0.2 is as follows.  The statement

    adjustable x = 3

  and the statements

    adjustable x
    x = 3

  now have the same effect (more consistent).  They both temporarily
  set the current value to 3 and leave the default value untouched.
  However, when the program finishes loading, SIMION now sets the
  default value for the adjustable variable to its current value.
  SIMION then resets its current value to the current value prior to
  loading except if the default value was changed.  CONCEPTUALLY YOU
  CAN THINK OF IT THIS WAY: DURING PROGRAM LOADING, THE PROGRAM -IN
  EFFECT- DEFINES THE DEFAULT VALUE, WHILE AT PROGRAM RUNNING THE
  PROGRAM MAY ONLY UPDATE (TEMPORARILY) AND ACCESS THE CURRENT VALUE.

  *Under the changed behavior, the end result of the typical usage
  given above is the same*, but the implementation is slightly
  differently.  During program loading, the current value temporarily
  changes to 3.  At the end of program loading, the default value is
  set to the then current value (3) and the current value is reset to
  the current value prior to loading (unless the default has changed).
  During the Fly'm, the current value is incremented.  At the end of
  the Fly'm the current value is reset to the current value prior to
  the Fly'm.

  The end results differs, however, under the new behavior for some
  more atypical cases such as in the trap example where adjustable
  variables are initially defined in one file (e.g. util.lua) and
  overriden by redefinitions in another file (e.g. inject.lua).

    -- util.lua file
    adjustable _mean_free_path = 4.0
    -- inject.lua file
    adjustable _mean_free_path = 1.0  

  Under the old behavior, when this is loaded, the default value
  changes to 4 and then to 1, which is ok.  However, if the user
  changes the current value in the Adjustable tab to, say, 8.0, then
  the current value specified by the user will always get reset to the
  default value on program reloading.  The first adjustable definition
  in util.lua temporarily resets the default value to 4.0 when it was
  previously most likely the 1.0 defined later.  SIMION sees that the
  default value has changed, so it **resets the current value to 4**
  (not wanted).  In inject.lua, this happens again and the current
  value is reset to 1.0.  So, the current value always becomes 1.0
  regardless what the user entered in the Variables tab.

  Under the new behavior, after loading, the default value becomes
  1.0, and the current value is reset to current value prior to
  loading (unless the default value changed).  This is the desired
  behavior.

  Consider this more atypical case:

    simion.workbench_program()
    adjustable x = 2
    x = 3
    function segment.other_actions()
      ...
    end

  Here, the second and third lines are both executed during program
  loading (not Fly'm).  Under the old behavior, after loading the
  default value becomes 2 and the current value permanently becomes 3.
  Under the new behavior, the default value becomes 3 and the current
  value remains unchanged (unless the default value changes).

  Consider this other more atypical case:

    simion.workbench_program()
    function segment.other_actions()
      adjustable linear_damping = 10
      print(linear_damping)
    end

  Here, the third line is executed during the Fly'm.
  Under the old behavior, during the Fly'm the default value
  becomes 10.  If the default value changes, the current value
  is changed to 10 until the end of the Fly'm, in which
  case it is reset to the value prior to the Fly'm.  This behavior
  is probably not so useful.  Under the new behavior, the
  current value changes to 10.

  If just this is done

    function segment.other_actions()
      adjustable linear_damping
      print(linear_damping)
    end

  Then under both the old and new behavior the default and current values
  are unchanged.

  Consider this:

    simion.workbench_program()
    adjustable x = 3
    adjustable y = x

  Initially, the default and current values of x and y are both 3.
  Now, say the user adjusts x to 4 and reloads the program by starting
  a new Fly'm.  Under the old behavior, the second line has no effect,
  but the third line sets the default value of y to 4.
  Under the new behavior, default and current values of both variables
  remain unchanged by the reloading.

  Changed in 8.0.2.

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