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# Alex Sha

##### Last seen: Today
136 total contributions since 2019

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How to fit complicated function with 3 fitting parameters using Least square regression
Hi, you may try to use "lsqcurvefit" command or curve fitting tool box (cftool), it is also better if you post data as well as k...

4 days ago | 0

| accepted

Why is this not working
There are another five more solutions: No. x1 x2 x3 x4 x5 x6 x7 x8 x9 1 300 200 200 0 0.0447213595499958 -0.0447213595499958 3...

15 days ago | 0

Fsolve complex results make no sense
Hi, Frederic Kluser, with your second case of Eq(9), I get the results below, all seem to be prefect: p: 1.79143003389998 p1_h...

25 days ago | 0

Optimization of 9 unknown with 9 nonlinear constraints by fmincom
one inequality constraint is: x(1)-x(2)+x(3)-x(4)+x(5)-x(6)+x(7)-x(8)+x(9)<=0 (1) while one of equality constraint is: J*(x...

28 days ago | 1

How to guess initialization parameters for non-linear curve fitting with nlinfit?
Hi, Aindrila, guessing the initial start value is always a difficult task since the local optimization algorithms are adopted in...

1 month ago | 0

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using least square fit to find the best fit parameters

1 month ago | 0

How to solve 3 non-linear equations with 3 unknowns?
One of numerical solution looks like: x: 4.49127153145489E-101 y: 0.0437692354838294 z: 867273686630772

1 month ago | 0

How can I fit this data?
Hi, toon, how about the model function below: z = (p1+p2*x+p3*x^2+p4*y+p5*y^2)/(1+p6*x+p7*x^2+p8*x^3+p9*y+p10*y^2); where x: s...

1 month ago | 0

How do I find the coefficients of a function for a curve fit?
The below should be the best solution: Root of Mean Square Error (RMSE): 0.0255893453091926 Sum of Squared Residual: 0.0471466...

1 month ago | 0

Matlab curve fitting two equations simultaneously with common arguments
Hi, Liu, your fitting functions are overdeterminted, there are multi-solutions: 1: Root of Mean Square Error (RMSE): 0.1634941...

1 month ago | 0

continuity of a fit function in different regions
Hi, the function below meets your requirements， with the derivative to be zero at x=1 y = p1+p2*(((x-p3)*(x+p4))^2)^p5; Root o...

1 month ago | 0

lsqcurvefit not adjusting some parameters as expected
The best solution seems to be: Root of Mean Square Error (RMSE): 8.58712889537096E-5 Sum of Squared Residual: 1.50943288116718...

1 month ago | 0

Fit multiple data with one mathmatical model/function
Hello, AHMED, your fit function is overdeterminted which will lead to multi-solutions, the parameter of "a1" is redundant: C=a1...

1 month ago | 1

How to fit a custom equation?
If don't care the type of fitting function, try the below function, much simple but with much better result: y = b1+b2*x^1.5+b3...

1 month ago | 0

Fitting a sigmoid curve using curve fitting tool box
Hi, Hair, the quailty of your data seems to be bad for sigmoid type of function. If take the function like: y = y0+a/(1+exp(-(x...

1 month ago | 1

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How can i solve the error "Reference to non-existent field 'xShape'. Error in finDiffEvalAndChkErr Error in finitedifferences'"
Hi, as my test, if c>0.367879, there is no solution for your equations.

2 months ago | 0

Error fsolve undefined function or variable x.
taking initial start-values as: x0=[6 0.5 150]; will produce: x1: 5.96 x2: 7.50486851347978E-7 x3: 152.194203428967

2 months ago | 1

Designing an iterative algorithm for a nonlinear system of equations
There are two set of solutions: 1 x1: 0.256953706774553 x2: -399.382730699003 x3: 0.0102597835062331 Fevl: 9.92301206481...

2 months ago | 0

Solving a system of 5 dependent non-linear equations
My pleasure, it is actually very challenging problem, hard to be solved by common software or algorithms.

2 months ago | 0

fsolve & linsqnonlin cant solve my equations
The unique stable results: x1: 0.231780000872077 x2: 0.040000000119062 x3: 0.508699999227432 x4: 0.00060000005989538 x5: 4....

2 months ago | 0

Solving a system of 5 dependent non-linear equations
Hi, if vt = 0.0257, the solution should be: m: 512.891368076595 rsh: -1.08505661410065 rs: 3.40678689852078 io: 0.8568128664...

2 months ago | 0

Solving a system of nonlinear equations with bounded variables
There are two solutions: 1: q_b: 0.305291000916417 q_v: 0.0179815487538954 q_lp: 0.237309452162523 y: 1.25168611470519 pr:...

2 months ago | 0

Curve fitting with constraints
Hellow, Paul, if adding one more parameter in your fitting function, i.e. y = a*exp(b*x) + c*exp(d*x)+f Then: from y(0) = 0, w...

2 months ago | 0

how to solve a system of non linear-equations
Hi, I get the solutions below: 1: r1: 0.0136978624480164 r2: -0.0529268624480211 c1: 23794.5028958407 c2: 1043438.64860562 ...

2 months ago | 0

No solution found when solving 3 non linear equations
Hi, all, how about the solutions below, from the numerical perspective： 1： x1: -5.21219473201765E21 x2: -0.279500437676178 x...

2 months ago | 0

Multiple equations solving in MATLAB
Hi, Golam, post out your problem, we may try.

2 months ago | 1

8 nonlinear equations, 8 unknowns - little luck with fsolve/vpasolve
Hi, Alex Tekin, you may try some solvers or software package with the ability of global optimization, i.e. Baron, Lingo, 1stOpt....

2 months ago | 1

| accepted