Brian Dunning's FileMaker Custom Functions

ErrorFunctionInverse ( x )

Calculates the inverse error function via Taylor series expansion

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Jeremy Bante   Jeremy Bante

http://github.com/jbante

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  Sample input:
List (
ErrorFunctionInverse ( -.8 ) ;
ErrorFunctionInverse ( -.6 ) ;
ErrorFunctionInverse ( -.4 ) ;
ErrorFunctionInverse ( -.2 ) ;
ErrorFunctionInverse ( 0 ) ;
ErrorFunctionInverse ( .1 ) ;
ErrorFunctionInverse ( .3 ) ;
ErrorFunctionInverse ( .5 ) ;
ErrorFunctionInverse ( .7 ) ;
ErrorFunctionInverse ( .9 )
)
  Sample output:
-.90619380243681129116239661400140183641072811603236
-.59511608144999483099716019972985021912702246342263
-.37080715859355792771730281906148776800110420959213
-.17914345462129167542107793245150434382489250138362
0
.0888559904942577
.27246271472675435351518042903635524518984326931916
.47693627620446987015027371023187301092338722790087
.73286907795921666827066321704975849515295969428148
1.16308715364904662588930164987257155615356517332946

  Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

Returns the inverse error function of x (commonly represented as erfinv(x) in other programming environments). The calculation happens by means of a Taylor/Maclaurin series expansion. The coefficients for the terms of the series are memoized in variables to improve performance in repeated calls to the function within the same local scope.

 

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