MATLAB Answers


How to curve fit following summation equation in MATLAB with given experimental data.

Asked by abxz
on 12 Nov 2019
Latest activity Edited by abxz
on 15 Nov 2019 at 15:31
a,k,c,b, and g are constants to be determined.


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Not able to write code.. will you please help with the code
@ Kalyan Acharjya, will you please help out with code
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3 Answers

Answer by Alex Sha on 13 Nov 2019
 Accepted Answer

d(K/ (1+exp(c-b*t)))/dt=k*exp(c-b*t)*b/sqr(1+exp(c-b*t)),so your fitting function become:
is the above correct? if yes, you may see the function is over-fit, that means the parameters will not be unique, one solution likes below:
Root of Mean Square Error (RMSE): 11257.9862380487
Sum of Squared Residual: 1647649303.76923
Correlation Coef. (R): 0.891727403408187
R-Square: 0.795177761989108
Adjusted R-Square: 0.726903682652144
Determination Coef. (DC): 0.795103266693536
F-Statistic: 7.64708134900884
Parameter Best Estimate
-------------------- -------------
a 67082.9685482823
k 2.55264230357405E16
c 39.1820152654189
b 0.0511178327965598
g 1.74671169710137E-249


Why you are providing the two answers?
You can add the modified answer as a comments in the first answer.
@ Alex Sha, Thanks a lot for your help.
will you please provide the code also.

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Answer by Alex Sha on 12 Nov 2019

Hi, Yadav, in your function "a*d/dt(k/1+exp(c-b*t))", what is "d/dt"? does "k/1" equal to "k"? Please describe clearly.


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@Alex Sha , will you please help out with code.
@Alex Sha , will you please help out with code.
@ Alex Sha , Please send code . I need code so if i have to do similar kind of fitting , i can take the help from the code.
Thank you.

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Answer by Alex Sha on 14 Nov 2019

Hi, Yadav, I actually use a software package other than Matlab, named 1stOpt, it is much easy for using without guessing initial start-values, since it adopts global optimization algorithm. The code looks like below:
Parameter a,k,c,b,g;
ConstStr f=a*(k*exp(c-b*t(i))*b)/(1+exp(c-b*t(i)))^2;
Variable t,z[OutPut],y;
StartProgram [Basic];
Sub MainModel
Dim as integer i, j, n
Dim as double temd1, temd2
for i = 0 to DataLength - 1
n = t(i)
temd1 = 0
for j = 0 to n
temd1 = temd1 + f
temd2 = 0
for j = 0 to n
temd2 = temd2 + g*y(j)
z(i) = temd1 + temd2
End Sub
a much better result:
Root of Mean Square Error (RMSE): 9901.69220512954
Sum of Squared Residual: 1274565610.8266
Correlation Coef. (R): 0.918681151445272
R-Square: 0.84397505802081
Adjusted R-Square: 0.791966744027747
Determination Coef. (DC): 0.841498837497943
F-Statistic: 9.7840155772957
Parameter Best Estimate
-------------------- -------------
a -277156.527610417
k -10698197.9029827
c 28.5533367811484
b 0.35649699061682
g 3.06293808255498E-8


@Alex Is this package supports by Matlab? You are giving multiple answers for same question. you can add extentions answer in the comment section of respective answer.
Sorry for giving multi-answers.
1stOpt is an independent software package I think, not the add-in or toolbox of Matlab.
@ Alex Sha , Thank you so much.

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