Used to mark questions about nonlinear differential equations, NonlinearModelFit, and related to nonlinear dynamics.
Questions tagged [nonlinear]
791 questions
6
votes
3 answers
Removing nonlinear terms
The following is a condensed version of a lengthy expression. My objective is to eliminate nonlinear terms from an expression.
The vector containing the variables is:
veclst = {Subscript[A, 11], Subscript[A, 13], Subscript[A, 15]};
The reduced form…
qahtah
- 1,397
- 6
- 14
4
votes
2 answers
Nonlinear model fit not working
Probably a very simple fix, but I'm trying to fit a simple exponential. Even when I put in good guesses, the model won't fit the data. Any suggestions?
<< StandardAtmosphere`
data = Table[{alt, MeanFreePath[alt Quantity[1, "Kilometers"]][[1]]},…
icebox207
- 77
- 5
3
votes
3 answers
NonlinearModelFit code
I have the following code, but I don't know how to use the NonlinearModelFit code to fit the data to plot the Gaussian curve:
Ph = 0.5;
N10 = 10;
bincoin10 = ListPlot[Table[{Nh,10*10*Ph^(Nh)*(1 - Ph)^(N10 - Nh)*N10!/((Nh!*(10-Nh)!))}, {Nh,0,10}]]
Shawn
- 45
- 1
- 3
2
votes
1 answer
Nonlinear frequency response
I am trying to reproduce the result of this paper, namely Figure 10 which depicts the solution of equation 64 given as,
qmax is the steady state solution of the oscillatory equation given. I tried to reproduce the result using the code below:
data…
qahtah
- 1,397
- 6
- 14
2
votes
1 answer
How to add measurement errors (or uncertainties) on NonlinearModelFit (with Weights)
I'd like to fit a Nonlinear curve to a dataset, which has an uncertainties vector associated. The problem is that I'd also like to add Weights to the fit. Lets say that my dataset is:
data={{-2., 1.00884}, {-1.5, 2.75486}, {-1., 4.00577}, {-0.5,
…
Fábio
- 133
- 5
2
votes
2 answers
Plot the results of a nonlinear system of equations
I have this system of four nonlinear equations:
the unknowns are a1, a2, gamma1 and gamma 2. all other parameters are known. What I want is to plot the a1 vs sigma2 as below:
I tried findinstance but it takes a lot of time to find the results for…
Soroush S.
- 21
- 4
2
votes
1 answer
NonlinearModelFit seems overly sensitive to small variation in a coefficient
The only difference between my code1 and code2 is the coefficient of Sin is 84.95 in the 1st case and 84.96 in the 2nd, I really wonder why such a small variation makes such a large difference in results.
code1 works perfectly, but code2 produces a…
Director.Jake
- 21
- 2
1
vote
1 answer
NonLinearModelFit is overlooping throught constraints
I have a NonLinearModelFit in which a constraint is this formula (I have added the Print function to test)
ximgConst[xs_Real, xt_Real, alpha_Real, tao_Real] :=
Print@NIntegrate[(xt - xs)*(2*Pi*freq*tao)^(1 - alpha)*
Cos[alpha*Pi/2]/(1 +
…
J.M.
- 11
- 2
1
vote
0 answers
Using Mathematica to solve a nonlinear system of parameters
I'm looking for some sets of solutions for this nonlinear system. I only have to respect the conditions, getting numerical values to use for another thing:
$\delta_1>10 |\lambda_1| (1)$
$\delta_2>10 |\lambda_2| (2)$
$\Delta_1>10 |\Omega_1|…
Flávio Oliveira Neto
- 11
- 1
1
vote
1 answer
Help with solving system of equations over complexes
Hi can you suggest me a way to Reduce/solve the following equation(analytic/numeric):
eqn= {-a1 + I (\[Pi] (((1/2 - I) + \[Pi]/3) Conjugate[
r1] + ((1/2 + I) + \[Pi]/3) Conjugate[r2]) +
3 \[Pi] (((1 - 2 I) + (2 \[Pi])/3) Conjugate[
…
Rupesh
- 887
- 5
- 10
1
vote
1 answer
Complex nonlinear equation solution
I am trying to find an analytic/numeric solution for a set of equations involving functions, summation, and complex quantities.
Definitions:
step = 1;
num = 15;
rho = Range[step , num, step];
theta = Most[Range[0, 2 Pi, 2 Pi/10]];
area[l_] := \[Pi]…
Rupesh
- 887
- 5
- 10
1
vote
1 answer
Problem with NonLinearModelFit when changing data sample area
It's a physics promblem, I want to confirm an integration without analytic solution to have the form of f[x]=k/x^2. The data set come from a NIntegration:
{xmin, xmax, xstep} = {2, 5000000, 100000};
ydata = Table[NIntegrate[((1 - x*Cos[a])*(x -…
user43887
- 11
- 3
0
votes
1 answer
i have this pitchfork bifurcation f=x^4-mx^3+x^2, is there a way to colour the equilibria according to their stability?
V = x^4 - m*x^3 + x^2
sol = Solve[D[V, x] == 0, x] // Simplify
Plot[{x/.sol[[1]],x/.sol[[2]],x/.sol[[3]]},{m,0.1,4}, PlotStyle->{Blue,Blue,Blue}]
as far as I'm concerned sol[[1]]=0 at first is stable, when m>mbif it becomes unstable
jason
- 1
0
votes
1 answer
Non-linear system of differential equation with stiff potential
I am trying a system of two differential equations that looks pretty simple, but with a potential varying a lot on a short period centered on 0. The definition of the potential followed by the attempt at solving the differential equation is
a0[y_]…
Free_ion
- 58
- 7
0
votes
0 answers
NonlinearModelFit reproducibility
I have a big data set about 10,000 points of 3 independent variables. I am fitting with NonlinearModelFit command. After this, I specified 3 values for three variables to model fit and it gave me a value (say 0.18).
Now, I repeat the test by taking…
george
- 71
- 4