Hi experts,
I met an incredible problem when use graph->Integral(). I integrate a graph from the first point to the third point using graph->Integral(0,2), then it return a value 0 but it should have not be zero. I have outputed the first, second and third point and find they are all larger than zero, so the integral should not be zero. the code I wrote and parts of output are given below. Hope you can help me resolve the problem. thank you.

Thank you Wile,
Now I realized that this function computes the area of the polygon enclosed by the points of the graph. This is not the function I wanna. I wanna integrate the graph from xlow to xup. Would you mind telling me how can I make it?