[MATLAB基础] 求助：如何确定自定义函数拟合时的参数初值？感谢！

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我做一个人口增长的拟合，在确定参数初值时遇到了严重的麻烦，求高手给与帮助！！！万分感谢！！！
以下是我写的程序：

>> t=[1790:10:2000];

>> population=[3.9 5.3 7.2 9.6 12.9 17.1 23.2 31.4 38.6 50.2 62.9 76.0 92.0 106.5 123.2 131.7 150.7 179.3 204.0 226.5 251.4 281.4];

>> ft=inline('a(1).*a(2)./(a(1)+exp(-a(3).*t).*a(2)-exp(-a(3).*t).*a(1))','a','t');

>> a=nlinfit(t,population,ft,[1 1 1])

Warning: Rank deficient, rank = 1, tol = 2.6167e-014.
> In nlinfit>LMfit at 296
In nlinfit at 168

Warning: Rank deficient, rank = 1, tol = 2.6050e-014.
> In nlinfit>LMfit at 296
In nlinfit at 168

Warning: Rank deficient, rank = 1, tol = 2.6038e-014.
> In nlinfit>LMfit at 296
In nlinfit at 168

Warning: The Jacobian at the solution is ill-conditioned, and some
model parameters may not be estimated well (they are not identifiable).
Use caution in making predictions.
> In nlinfit at 225
a =
1.0000 94.7727 1.0000

当然[1 1 1]是我瞎写的，显然最后的结果不对啊！但到底应该是什么呢？怎么确定？:handshake