[x,resnorm] = lsqcurvefit(...) returnsthe value of the squared 2-norm of the residual at x: sum((fun(x,xdata)-ydata).^2).[x,resnorm,residual] = lsqcurvefit(...) returnsthe value of the residual fun(x,xdata)-ydata atthe solution x.x是拟合出来的系数，resnorm是残差，residual是残差向量...
