Output 是所谓的拟合卡方值，这是一种流行的选择拟合统计.不过，对于非线性拟合来说有些问题.您可以直接查看残差(out.delta 用于 X 残差，out.eps 用于 Y残差).如链接论文中所建议的那样，实施交叉验证或引导方法来确定拟合优度，留给读者作为练习.

The res_var attribute of the Output is the so-called reduced Chi-square value for the fit, a popular choice of goodness-of-fit statistic. It is somewhat problematic for non-linear fitting, though. You can look at the residuals directly (out.delta for the X residuals and out.eps for the Y residuals). Implementing a cross-validation or bootstrap method for determining goodness-of-fit, as suggested in the linked paper, is left as an exercise for the reader.