root fit

TGraphErrors fit

以下在链接的代码1165行
///
/// In case of a TGraphErrors object, when x errors are present, 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 then computed as the sum of the quantity below at each point:
///
/// \f[
/// \frac{(y-f(x))^{2}}{ey^{2}+(\frac{1}{2}(exl+exh)f’(x))^{2}}
/// \f]
///
/// where x and y are the point coordinates, and f’(x) is the derivative of the
/// function f(x).