Statistical Volatility - Extreme Value Method

/*********************************Provided By:      eSignal (Copyright c eSignal), a division of Interactive Data     Corporation. 2009. All rights reserved. This sample eSignal     Formula Script (EFS) is for educational purposes only and may be     modified and saved under a new file name.  eSignal is not responsible    for the functionality once modified.  eSignal reserves the right     to modify and overwrite this EFS file with each new release.Description:            Statistical Volatility - Extreme Value Method     Version:            1.0  05/22/2009     Formula Parameters:                     Default:    nLength                             30    Notes:    This indicator used to calculate the statistical volatility, sometime     called historical volatility, based on the Extreme Value Method.    Please use this link to get more information about Volatility. **********************************/var fpArray = new Array();var bInit = false;function preMain() {    setStudyTitle("Statistical Volatility - Extreme Value Method");     setCursorLabelName("Xtrme Vlty");    var x = 0;    fpArray[x] = new FunctionParameter("nLength", FunctionParameter.NUMBER);    with(fpArray[x++]) {        setLowerLimit(1);        setDefault(30);    }    }var xVolatilityExtVal = null;function main(nLength) {var nBarState = getBarState();var nVolatilityExtVal = 0;    if (nBarState == BARSTATE_ALLBARS) {        if (nLength == null) nLength = 30;    }        if (bInit ==  false) {        xVolatilityExtVal = efsInternal("Calc_VolatilityExtVal", nLength);        bInit = true;    }    nVolatilityExtVal = xVolatilityExtVal.getValue(0);    if (nVolatilityExtVal == null) return;    return nVolatilityExtVal;}var bSecondInit = false;var xClose = null;var xMaxC = null;var xMinC = null;var xMaxH = null;var xMinL = null;function Calc_VolatilityExtVal(nLength) {var nRes = 0;var i = 0;var SqrTime = Math.sqrt(253 / nLength);    if (bSecondInit == false) {        xClose = close();        xMaxC = upperDonchian(nLength, xClose);        xMinC = lowerDonchian(nLength, xClose);        xMaxH = upperDonchian(nLength);        xMinL = lowerDonchian(nLength);        bSecondInit = true;    }    if (xMaxC.getValue(0) == null) return;    nRes = ((0.6 * Math.log(xMaxC.getValue(0) / xMinC.getValue(0)) * SqrTime) +            (0.6 * Math.log(xMaxH.getValue(0) / xMinL.getValue(0)) * SqrTime)) * 0.5;    if (nRes < 0) nRes = 0.0;    if (nRes > 2.99) nRes = 2.99;    return nRes;}