各位大神，我在用matlab中的cftool拟合非线性函数，得到的cfit如何进行函数操作，求导等。

PS 我试了提取出各个系数，构造函数，然后对构造的函数进行求导，但结果不理想，得到的函数g 在相同的x值处 函数值很不好，是exp的一个表示，为

g(0)

ans =

(81237295002235*exp(-546461714598735789728624069099536/6544490893783104415829273208081))/140737488355328 + (2495506857451569*exp(-22784005895725160164421051430121/339550163399717490602339615134096))/140737488355328 + (1158821406772579*exp(-124115814564550127768460048600676/23029478501256146398011601513041))/281474976710656 + (2946948027047363*exp(-1357341483970986610734701600625/415545017388687786102707772649))/562949953421312

而f

>> f(0)

ans =

16.799

下面是cfit函数的表示

f =

General model Gauss5:

f(x) =

a1*exp(-((x-b1)/c1)^2) + a2*exp(-((x-b2)/c2)^2) +

a3*exp(-((x-b3)/c3)^2) + a4*exp(-((x-b4)/c4)^2) +

a5*exp(-((x-b5)/c5)^2)

Coefficients (with 95% confidence bounds):

a1 =       5.235

b1 =       115.9

c1 =       64.12

a2 =           0

b2 =       221.1

c2 =       1.222

a3 =       17.73  (15.58, 19.88)

b3 =       135.7  (37.03, 234.3)

c3 =       523.7  (307.9, 739.5)

a4 =      0.5772  (0.1464, 1.008)

b4 =       332.2  (311.5, 352.9)

c4 =       36.35  (1.694, 71.02)

a5 =       4.117  (2.648, 5.586)

b5 =        1267  (939, 1594)

c5 =       545.6  (-342.1, 1433)

>> diff(f)

Error using diff

Function 'diff' is not supported for class 'cfit'.