用lsqcurvef​it没能拟合出参数，​求各位指教。代码如下​。

function f=XU(x,data)

XOD=data(1,:);

UA=data(2,:);

f=x(1)*(1+(x(2)*XOD)./(XOD+x(3)))-x(4)*UA

clc;

XOD=[13.920855 16.137478 18.802967 21.793845 19.668576 22.731821 23.275489 28.416212 30.66387];

UA=[34.723876 114.1186 91.402479 79.854949 77.639966 92.321463 104.54 96.047456 106.25276];

ydata=[10.4299978000000,-1.45032320000000,-0.425708066666667,0.0532981666666667,-0.00421063333333341,0.138016733333333,-0.0427233666666666,-0.0627239250000000,-0.0827244833333334];

data=[XOD;UA];

option=optimset('MaxFunEvals',50000000);

x0=[0.5 0.5 0.1 1];

[a,resnorm]=lsqcurvefit(@XU,x0,data,ydata,[0 0 0 0],[],option);

出现在命令栏中的提示如下：

Local minimum possible.

lsqcurvefit stopped because the final change in the sum of squares relative to

its initial value is less than the default value of the function tolerance.

<stopping criteria details>

Answer 1

[bipeh]

如果要求都大于0，加一句：ParameterDomain = [0,];

均方差(RMSE):1.50695589848579

残差平方和(SSE):20.43824471983

相关系数(R): 0.895278856473547

相关系数之平方(R^2): 0.801524230848583

确定系数(DC): 0.801524230848583

卡方系数(Chi-Square): 9.45032996543549

F统计(F-Statistic): 8.39733068571794

参数 最佳估算

---------- -------------

x1 1.89870321365435

x2 5.89251645596632

x3 3.8799368609697E-15

x4 0.137066729882979