/**
 * Holt's Exponential Smoothing
 * @returns {object} Object containing the forecast points, the residuals, the sum of squares of the residuals and the factor
 */
ssci.fore.holt = function(){
    var data = [];
    var dataArray = [];
    var numPoints = 0;
    var output = [];
    var resids = [];
    var sumsq  = 0;
    var factor = 0.3;
    var trend  = 0.3;
    var x_conv = function(d){ return d[0]; };
    var y_conv = function(d){ return d[1]; };
    var l=[];
    var t=[];
    var funcs_T = {
        '1': t1,
        '2': t2,
        '3': t3,
        '4': t4
    };
    var funcT = '1';    //Function to use to calculate the starting value of

    /**
     * Initial average difference between first three pairs of points
     */
    function t1(){
        return (1/3)*(dataArray[1][1]-dataArray[0][1])+(dataArray[2][1]-dataArray[1][1])+(dataArray[3][1]-dataArray[2][1]);
    }
    /**
     * Calculate trend for entire series and multiply by average distance between points
     */
    function t2(){
        return ssci.reg.polyBig(dataArray,1).constants[1] * ((dataArray[numPoints-1][0]-dataArray[0][0])/(numPoints-1));
    }
    /**
     * Trend for first to second point
     */
    function t3(){
        return dataArray[1][1]-dataArray[0][1];
    }
    /**
     * Trend between first and last point
     */
    function t4(){
        return (dataArray[numPoints-1][1]-dataArray[0][1])/(numPoints-1);
    }

    function retVar(){
        var i;

        //Clear output array - needed to stop output growing when function called repeatedly
        output = [];

        //Create array of data using accessors
        dataArray = data.map( function(d){
            return [x_conv(d), y_conv(d)];
        });
        numPoints = dataArray.length;

        //Push first value to dataArray
        output.push(dataArray[0]);

        //Generate starting value for l - first value of dataArray
        if(l.length===0){
            l.push(dataArray[0][1]);
        }

        //Generate starting value for t - initial average difference between first three pairs of points
        if(t.length===0){
            t.push(funcs_T[funcT]);
        }

        //Calculate new values for level, trend and forecast
        for(i=1;i<(numPoints);i++){
            l.push(factor*dataArray[i][1]+(1-factor)*(l[i-1]+t[i-1]));
            t.push(trend*(l[i]-l[i-1])+(1-trend)*t[i-1]);
            //Create forecasts - current forecast is based on last periods estimates of l(evel) and t(rend)
            output.push([dataArray[i][0], l[i-1]+t[i-1]]);
        }

        //Calculate residuals
        sumsq=0;
        for(i=1;i<numPoints;i++){
            resids.push(dataArray[i][1]-output[i][1]);
            sumsq += Math.pow(dataArray[i][1]-output[i][1],2);
        }

    }

    /**
     * Get or set the initial value for the level
     * @param {number} [value] - The value for the level
     * @returns Either the value for the level or the enclosing object
     */
    retVar.initialLevel = function(value){
        if(!arguments.length){ return l[0]; }
        l = [];

        l.push(value);

        return retVar;
    };