How to add a trendline to my graph in qt creator?-CodePudding

I want to add a trendline to my graph in qt creator, but I dont know how , can someone tell me a way to do that in qt creator c .Literally I have no idea on how to plot a trendline on a line graph,pls suggest me a method.

CodePudding user response：

By the way it's not a specific QtCreator question. Did you know how to compute a trendline mathematically ?

Slope:

Offset:

Trendline formula:

where

a is slope
x is the horizontal axis value
b is the Y-intercept

Normally you have sccattered data that makes up your graph. No matter if you use QtWidget or QML you can follow these steps.

First, find the average of the x values and the average of y values.
Next, find the distance between each x value and the average of the x values, and the distance between each y value and the average of the y values.
Then multiplying (x(i) - X(i)) by (y(i) - Y(i)) , and multiplying (x(i) - X(i)) by itself.
Get the sum of first formula ((x(i) - X(i)) by (y(i) - Y(i))) and sum of second formula ( (x(i) - X(i)) )
Find the slop a by dividing first formula sum by second formula sum.
Get the average value of x and y and find b value using trendline formula : y = ax b so b = y - ax

Then you have everything you want to apply your trendline equation

Using your equation, you could now draw your line trend on your QCustomPLot using two point:

QCPItemStraightLine *trendLine = new QCPItemStraightLine(customPlot);
trendLine->point1->setCoords(x, y);  // location of point 1 in plot coordinate
trendLine->point2->setCoords(xx, yy);  // location of point 2 in plot coordinate