/** 
	linear fit to active data between specified range by row numbers, a red fit curve is added to the graph
Parameters:
	nLower = lower index to start from or -1 to start from the lower bound.
	nUpper = upper index to end at, or -1 to end at the upper bound.
	nFitXRange = -1 to fill entire X range, 0 to be from x1 to x2, >0 percent extra outside x1 x2
*/ 
void fitlr(int nLower = -1, int nUpper = -1, int nFitXRange = 0)
{
	string strCuvName = Project.ActiveCurveBase().GetName();
	if(strCuvName.IsEmpty())
		return;
	GraphLayer glyr = Project.ActiveLayer();
	if(glyr == NULL)
		return;// we only will fit a graph
	
	int nNumMissingInCopy, nSrcOffset;
	// create a temp copy of Active curve to ensure data type is double and original range is not modified
	Curve cc(Project.ActiveCurveBase(), nNumMissingInCopy, nSrcOffset, 						
		CURVECOPY_SCAN_OVER_MISSING_FROM_LEFT | CURVECOPY_SCAN_OVER_MISSING_FROM_RIGHT | CURVECOPY_SKIP_MISSING_INSIDE,
		nLower, nUpper); 
	
	double coeff[2];
	fitpoly(cc, 1, coeff); // using built-in simple fitting function, sorry, no stats report	
	
	// generate fit curve
	double x1, x2;
	
	if(nFitXRange < 0) // span entire x axis
	{
		x1 = glyr.X.From;
		x2 = glyr.X.To;
	}
	else // use data x range, with possible wider X range
	{
		x1 = Curve_x(&cc, 0);
		x2 = Curve_x(&cc, cc.GetUpperIndex());
		double dx = (x2-x1) * nFitXRange/100.0;
		x1 -= dx;
		x2 += dx;
	}
	Worksheet wksFit;
	wksFit.Create(NULL, CREATE_HIDDEN);
	wksFit.SetSize(-1,0);// empty all cols
	wksFit.AddCol("FitX");
	wksFit.AddCol("FitY");
	wksFit.Columns(0).SetType(OKDATAOBJ_DESIGNATION_X);	
	wksFit.Columns(1).SetType(OKDATAOBJ_DESIGNATION_Y);
	Dataset fitx(wksFit, 0);
	Dataset fity(wksFit, 1);
	int nFitPts = 20;// generate fit curve of 20 pts
	fitx.SetSize(nFitPts);
	fity.SetSize(nFitPts);
	vector vData;
	vData.Data(0,nFitPts-1); // Generate 0, 1,2,... nFitPts 
	fitx = x1 + vData * (x2-x1) / (nFitPts - 1);
	fity = coeff[0] + coeff[1] * fitx;
	Curve cfit(wksFit, 0, 1);
	add_curve_to_graph_layer(cfit, glyr, 1, false, IDM_PLOT_LINE);
}