如何仅使用最后一条情节线后面的数据来计算高图中的预测（预测）？

Question

I have a code for standard area-spline highchart where I made a function for prediction based on previous data. Prediction / forecasting is showing next 4 values in a trendline where the first prediction point is counting with real data, second point with real data plus first prediction point and the next two points about the same plus previous predictions. Otherwise it would be only a line with same values. But my data are increasing so the forecasting must be about the same.

Data in highchart are connected to Microsoft SQL Server.

Prediction is based on this code, just with few changes: Forecast formula from Excel in Javascript

The highchart is now showing increasing data (values of resistance) as a decimal in yAxis and datetime in xAxis. Prediction is working as well but the thing is that not all data are relevant.There is always a point which is very different (lower than previous) and thats the place from where I need to count new prediction. The plotline is generated in the last high value, then starting the new (low) - and that is from where I need to count.

So here is what I do have:

-the function 'average' is counting average from values

-second function 'forecast' as you can expect is counting the forecasting (based on the code from link above)

-third function 'test' is already putting all together

-the 'results' (2,3,4) are the counted points of prediction

-'vlastnidata' are the data from mssql

-'datumek' is for the date

Now the condition for plotline (as you can see there) is that the previous point in chart must be 20 higher and then the plotline is generated - this is also working, just need to find a way how to count only with new data behind the plotline.

And here you can reach the connection function to mssql in php - if needed Is there a way how to dynamically create a plotline in highchart when the value is lower than previous one?

As I said everything is working, plotlines and the prediction. But to see clear prediction I need to count only with relevant data.

Hope everything is clear. Thank you in advance for any recommendations.

function average(ar) 
{
    var r=0;
    for (i=0;i<ar.length;i++)
    {
        r = r+ar[i];
    }
    return r/ar.length;
}

function forecast(x, ky, kx)
{   
    var i=0, nr=0, dr=0,ax=0,ay=0,a=0,b=0, result=0;                   
    ax=average(kx);
    ay=average(ky);
    for (i=0;i<kx.length;i++)
    {
        nr = nr + ((kx[i]-ax) * (ky[i]-ay));
        dr = dr + ((kx[i]-ax)*(kx[i]-ax))
    }
    b=nr/dr;
    a=ay-b*ax;
    result = (a+b*x);
    return result;                  
}   

function test(container,nazev,rtop,vlastnidata,colorSeries)
{       
    var result = 0, result2 = 0, result3 = 0, result4 = 0, datumek=[],hodnoty=[];
    for (a=0;a<vlastnidata.length;a++)
    {
        datumek[a]=vlastnidata[a][0];
        hodnoty[a]=vlastnidata[a][1];
    }
    kalkulace=(datumek[vlastnidata.length-1]-datumek[vlastnidata.length-2]);
    hodnoty_nove=hodnoty;
    datumek_nove=datumek;
    result = forecast((datumek[vlastnidata.length-1]+kalkulace), hodnoty, datumek);
    hodnoty_nove[hodnoty_nove.length]=result;
    datumek_nove[datumek_nove.length]=(datumek[vlastnidata.length-1]+kalkulace);
    result2 = forecast((datumek[vlastnidata.length-1]+2*kalkulace), hodnoty_nove, datumek_nove);
    hodnoty_nove[hodnoty_nove.length]=result2;
    datumek_nove[datumek_nove.length]=(datumek[vlastnidata.length-1]+2*kalkulace);
    result3 = forecast((datumek[vlastnidata.length-1]+3*kalkulace), hodnoty_nove, datumek_nove);
    hodnoty_nove[hodnoty_nove.length]=result3;
    datumek_nove[datumek_nove.length]=(datumek[vlastnidata.length-1]+3*kalkulace);
    result4 = forecast((datumek[vlastnidata.length-1]+4*kalkulace), hodnoty_nove, datumek_nove);


    Highcharts.chart(container, {chart: {type: 'areaspline',

    events: {   
                load:function(){
                    let points = this.series[0].points;
                    let plotLines = [];
                    console.log(this)
                    let previousPoint = points[0];
                    points.forEach(function(point) {

                        if(point.y < previousPoint.y/100*80) {
                            plotLines.push({
                                value: previousPoint.x,
                                color: 'red',
                                width: 3
                            });
                        }                        
                        previousPoint = point;
                    });
                    this.xAxis[0].update({
                        plotLines: plotLines
                    })
            }
        }
    },      
            title: {text: 'Average of resistance per month, '+rtop},
            legend: {layout: 'vertical',
                    align: 'left',
                    verticalAlign: 'top',
                    x: 150,
                    y: 100,
                    floating: true,
                    borderWidth: 1,
                    backgroundColor: (Highcharts.theme && Highcharts.theme.legendBackgroundColor) || '#FFFFFF'},            
            xAxis: { type: 'datetime'},
            yAxis: {title: {text: 'Resistance: in ohms'}},
            tooltip: {shared: true,valueSuffix: ' ohms',valueDecimals: 2},
            credits: {enabled: false},
            plotOptions: {areaspline: {fillOpacity: 0.5}},
            series: [{  name: nazev, 
                        color: colorSeries,
                        data: vlastnidata}, 
                        {name: 'Prediction', 
                        color: '#001a33',                   
                        data: [[(datumek[vlastnidata.length-1]+kalkulace),result], [(datumek[vlastnidata.length-1]+2*kalkulace),result2], [(datumek[vlastnidata.length-1]+3*kalkulace),result3], [(datumek[vlastnidata.length-1]+4*kalkulace),result4]]
            }]
    });                            
}