Positive Volume Index

/*********************************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:            Positive Volume Index    Version:            2.0  05/28/2009 Formula Parameters:                     Default:    EMA_Len                             255    Notes:    The theory behind the indexes is as follows: On days of increasing volume,     you can expect prices to increase, and on days of decreasing volume, you can     expect prices to decrease. This goes with the idea of the market being in-gear     and out-of-gear. Both PVI and NVI work in similar fashions: Both are a running     cumulative of values, which means you either keep adding or subtracting price     rate of change each day to the previous day`s sum. In the case of PVI, if today`s     volume is less than yesterday`s, don`t add anything; if today`s volume is greater,     then add today`s price rate of change. For NVI, add today`s price rate of change     only if today`s volume is less than yesterday`s.**********************************/var fpArray = new Array();var bInit = false;function preMain(){    setStudyTitle("Positive Volume Index");    setCursorLabelName("PVI",0);    setDefaultBarFgColor(Color.red,0);    setCursorLabelName("EMA",1);    setDefaultBarFgColor(Color.blue,1);    var x = 0;    fpArray[x] = new FunctionParameter("EMA_Len", FunctionParameter.NUMBER);    with(fpArray[x++]) {        setLowerLimit(1);        setDefault(255);    }    }var xPVI = null;var xPVI_EMA = null;function main(EMA_Len) {var nBarState = getBarState();var nPVI = 0;var nEMA = 0;    if (nBarState == BARSTATE_ALLBARS) {        if(EMA_Len == null) EMA_Len = 255;	}	if (bInit == false) {        xPVI = efsInternal("Calc_PVI");        xPVI_EMA = ema(EMA_Len, xPVI);        bInit = true;	}    nPVI = xPVI.getValue(0);    nEMA = xPVI_EMA.getValue(0);    if (nEMA == null) return;	return new Array(nPVI, nEMA);}var bSecondInit = false;var xROC = null;var xVolume = null;function Calc_PVI() {var nRes = 0;var nRef = ref(-1);    if (bSecondInit == false) {        xROC = roc(1);        xVolume = volume();        bSecondInit = true;    }	if (xROC.getValue(-1) == null) return;	if(xVolume.getValue(0) > xVolume.getValue(-1)) {		nRes = nRef + xROC.getValue(0);    	} else {        nRes = nRef;    }	    return nRes;}