TGraphErrors can define x errors, how to write a fcn to fit it?
When you call TGraphErrors::Fit (ie TGraph::Fit) the errors in x and y
are taken into account. See function GraphFitChisquare in TFitter
// In case of a TGraphErrors object, ex, the error along x, is projected
// along the y-direction by calculating the function at the points x-exlow and
// x+exhigh.
//
// The chisquare is computed as the sum of the quantity below at each point:
//
// (y - f(x))**2
// -----------------------------------
// ey**2 + ((f(x+exhigh) - f(x-exlow))/2)**2
//
// where x and y are the point coordinates.
//
// In case the function lies below (above) the data point, ey is ey_low (ey_high).
Rene
Thanks!