Curve fitting tool with 4 variables

I'm trying to predict soil respiration using 4 known vectors (x, y, z, and k) using the equation:

k = a*exp(b*x)*exp(c*y+d*y^2)+e*z+f

I tried looking online, but each problem uses 2 or 3 variables from the curve fitting tool. How can I do 4 variables?

Thanks in advance for any help.

Answer 1

[Alex Sha]

Attach your data file please.

[Mahesh Karki]

Hi Alex,

I have the same question and I have attached the data file below.

Here,

X1, X2 and X3 are the Independent Variable while Y1 is the dependent Variable and I don't have the fit equation.

I have also read the Matlab answers in similar topics, link atatched below:

https://www.mathworks.com/matlabcentral/answers/398161-can-i-make-curve-fitting-equation-for-more-than-5-variables-my-data-points-of-5-variable-is-more-th

https://www.mathworks.com/matlabcentral/answers/213867-how-to-curve-fit-4d-data

Do you have any suggestions?

Mahesh

[Yueqian Ma]

Like what the previous comments said, if you don't have a model, then you can't find any unknowns within the equation because there's literally an infinite amount of fits. I suggest you use the regression learner app in matlab to train and find a suitable model.

https://www.mathworks.com/help/stats/train-regression-models-in-regression-learner-app.html

Answer 2

[Alex Sha]

Hi, Mahesh, if you don't care the formation of the fitting equation, try the follows:

y = sin((((((p1-x3)^2)*x3)/(((x3^2)^(x2^p2))/exp(sin(((p3/(1+x3)^0.5)/(1+p4/x1))/(p5/(1-x3))))))*((1+x1)^0.5+x2^2))/(1/(p6-x2)^2))-(1/(p7+x2)-(1+p8/x3)+(x1+1)^p9);

Root of Mean Square Error (RMSE): 0.000948905304490633

Sum of Squared Residual: 1.08050553226855E-5

Correlation Coef. (R): 0.999562780052203

R-Square: 0.999125751265689

Adjusted R-Square: 0.998626180560369

Determination Coef. (DC): 0.999121540217668

Chi-Square: 1.52267545487959E-5

F-Statistic: 428.261316945475

Parameter Best Estimate

---------- -------------

p1 4.60817694964176

p2 0.774217015206445

p3 -125.052492026267

p4 98.1254106271433

p5 0.61282127680523

p6 2133.5891967895

p7 -7.82339269347936

p8 -2.25961768228283

p9 -0.56287172661848

[Mahesh Karki]

Hi Alex,

Thanks for your solution, I am interested to know how you find the fit equation, can you share the script.

Mahesh

Answer 3

[Ashok Kurakula]

Hi Alex,

Appriciate !!

In whole seach of mine, I didn't see one helping curve fitting more than 3 variables, you are the one who puts up sollution.

I do have the similar work for dynamically varing data, since data would keep chaging single equation wouldn't help me. I have 3 indipent variables and 1 dependent variable.

Great, if you could help me here. I would not need the code as on, but path to get a solution for my problem.

Thanks & Regards,

Ashok Kurakula.

[Alex Sha]

My Pleasure