曲线拟合求参数问题。

过路的大神帮帮忙

dat=importdata('data.txt');

n=length(dat);

x=dat(:,2);

y=dat(:,4);

y1=dat(:,5);

a0=[0 0 0 0];

a=lsqcurvefit('cepian',a0,x,y)这是主程序

函数程序为

function y=cepian(a,x)

Fz=2000;

uy=a(1)+a(2)*Fz+a(3)*Fz^2;

E1=0.5/(1+exp(-(Fz-a(1))/a(2)));

qy=a(4)*tan(x)/(uy*Fz);

z=-abs(qy)-E1*(abs(qy.^2))-(E1^2+1/12)*(abs(qy.^3));

Fy=1-exp(z);

y=(-qy/(abs(qy)))*uy*Fz*Fy;

总是出错如下

dat=importdata('data.txt');

n=length(dat);

x=dat(:,2);

y=dat(:,4);

y1=dat(:,5);

a0=[0 0 0 0];

a=lsqcurvefit('cepian',a0,x,y)

Warning: Rank deficient, rank = 0, tol = NaN.

> In cepian at 8

In lsqcurvefit at 209

??? Error using ==> snls at 46

Objective function is returning undefined values at initial point.lsqcurvefit cannot continue.

Error in ==> lsqncommon at 149

[xC,FVAL,LAMBDA,JACOB,EXITFLAG,OUTPUT,msgData]=...

Error in ==> lsqcurvefit at 258

[xCurrent,Resnorm,FVAL,EXITFLAG,OUTPUT,LAMBDA,JACOB] = ...

求神助啊

Answer 1

[koneb]

把你的初值带入函数，得到Nan才引起了这个问题，只要修改一下a0的初始值，使函数中分母不为0即可，修改后程序如下：

%% 清空环境变量
close all; clear; clc;

%% 主程序
dat=importdata('data.txt');
n=length(dat);
x=dat(:,2);
y=dat(:,4);
y1=dat(:,5);
a0=[0 0 0 1];
a=lsqcurvefit('cepian',a0,x,y)