主要是数学排列

>> t=0:30;

>> x=[107.507 109.300 111.026 112.704 114.333 115.823 117.171 118.517 119.850 121.121 122.389 123.626 124.761 125.786 126.743 127.627 128.453 129.227 129.988 130.756 131.448 132.129 132.802 133.450 134.091 134.735 135.404 136.072 136.782 137.462 138.271];

>> syms c d

>> [c,d]=solve(c/(1+(c/107.507-1)*exp(-5*d))==115.823,c/(1+(c/107.507-1)*exp(-8*d))==119.850,c,d)；

>> c=double(c)

c =

           109.738281373644 -      1.60177395988749i

>> d=double(d)

d =

         -0.150875720473954 -      2.06096070058854i

>> b0=[c,d]；

>> [b,r,j]=nlinfit(t,x,fun,b0);

警告: 秩亏，秩 = 1，tol =  5.675835e-13。 

> In nlinfit>LMfit (line 587)

  In nlinfit (line 284)

警告: 秩亏，秩 = 1，tol =  4.209312e-13。 

> In nlinfit>LMfit (line 587)

  In nlinfit (line 284)

警告: 秩亏，秩 = 1，tol =  4.033439e-13。 

> In nlinfit>LMfit (line 587)

  In nlinfit (line 284)

警告: 秩亏，秩 = 1，tol =  4.015428e-13。 

> In nlinfit>LMfit (line 587)

  In nlinfit (line 284)

警告: Some columns of the Jacobian are effectively zero at the solution, indicating that the

model is insensitive to some of its parameters.  That may be because those parameters are not

present in the model, or otherwise do not affect the predicted values.  It may also be due to

numerical underflow in the model function, which can sometimes be avoided by choosing better

initial parameter values, or by rescaling or recentering.  Parameter estimates may be

unreliable. 

> In nlinfit (line 381)