' Copyright (c) 2011-2013 Claude Rubinson <cjr@grundrisse.org>
'
' Licensed under the Apache License, Version 2.0 (the "License"); 
' you may not use this file except in compliance with the License.
' You may obtain a copy of the License at
'
'   http://www.apache.org/licenses/LICENSE-2.0
'
' Unless required by applicable law or agreed to in writing, software
' distributed under the License is distributed on an "AS IS" BASIS,
' WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
' implied.  See the License for the specific language governing
' permissions and limitations under the License.

Function FUZZ(value, lower_thresh, crossover, upper_thresh)

    ' FUZZ - calibrate fuzzy-sets for QCA

    ' This function implements the "direct" method of transforming an
    ' interval-ratio variable into a fuzzy set, as described in Ragin,
    ' Charles C. (2008) _Redesigning Social Inquiry_, Chapter 5
    ' ("Calibrating Fuzzy Sets")

    ' To use, enter "=FUZZ(value, lower_thresh, crossover, upper_thresh)"
    ' in a cell, parameters may be literals or cell references.  Note that
    ' the FUZZ function will NOT be available in the Function Wizard; neither
    ' can it be specified as part of a formula within the Function
    ' Wizard.  (If somebody knows how to implement this, please contact me.)

    ' To install as an OpenOffice/LibreOffice Calc macro:
    '
    ' In Calc, "Tools" -> "Macros" -> "Organize Macros" 
    '    -> "OpenOffice (or LibreOffice) Basic"
    '
    ' In the dialog box that opens, navigate to "My Macros" -> "Standard"
    '    -> "Module1" and click "Module1" to highlight it.  Click "Edit".
    '
    ' Paste the contents of this file to the end of the window that opens 
    ' (from the "Function FUZZ" statement above through "End Function", below)
    '
    ' Save the file and close it.
    '
    ' The FUZZ function should now be available in all instances of Calc (for
    ' your user).

    scalar_above = 3.0/(upper_thresh - crossover)
    scalar_below = -3.0/(lower_thresh - crossover)
    scalar_at = 0

    deviation = value - crossover
    if deviation < 0 then
		log_odds = deviation * scalar_below
    elseif deviation = 0 then 
        log_odds = deviation * scalar_at
    else  ' deviation > 0
        log_odds = deviation * scalar_above
    endif

    ' I don't know how to generate a proper error
    if (upper_thresh <= crossover) or (crossover <= lower_thresh) then
		FUZZ = "#Err1"
    else
        FUZZ = exp(log_odds)/(1+(exp(log_odds)))
    endif

End Function