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Questions tagged [stiffness]

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3 votes
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Dealing with stiff differential equations in NDSolve

I have a problem with solving the following system of differential equations : $$\frac {d^2 f (x)} {dx^2} + \frac {1} {x}\frac {df (x)} {dx} = \frac {f (x)} {x^2} + f^3 (x) + f (x) g^2 (x) - f (x)...
ZaraReinm.'s user avatar
2 votes
1 answer

Solving a ODE (Peeble's Equation) with initial condition a the maximum input range

I have a differential equation which is, $$ \frac{d X_e}{dz} = \frac{C_r(z)}{H(z)}\times \frac{1}{(1+z)}\Big[\frac{38\eta T^3}{25\pi^2}\alpha (T)X_e^2 - b(T)(1 - X_e) \Big] $$ Where $$ \alpha(T) = \...
Kazi Abu Rousan's user avatar
2 votes
1 answer

NDSolve::ndcf: Repeated convergence test failure; unable to continue

I have been trying to solve this system of differential equations: ...
Prokopii Anempodistov's user avatar
1 vote
3 answers

NDSolve producing oscillatory results

NDSolve producing very oscillatory solutions even after not having any large numbers or warning/errors ...
user105697's user avatar
0 votes
0 answers

NDSolve returns stiff problem and forces extrapolation which gives unreasonable result

I am trying to solve a first order ODE using ParametricNDSolve for getting particle trajectory in a flow around an obstacle. I got an error message that "At t == 221.96028149270003`, step size is ...
PKD's user avatar
  • 31
0 votes
0 answers

Stiffness or singularity in NDSolve for a system of equations with switchpoint

I am trying to solve the following set of equations: ...
Charles's user avatar
  • 73
1 vote
0 answers

Stiffness problem which abruptly stops the evaluation

We have a Lagrangian and we found the EOM. We need to solve the EOM and find the Phase-space plot. However, we are facing a stiffness problem which abruptly stops the evaluation (...
user444's user avatar
  • 2,550
1 vote
1 answer

NDSolve stiff system of ODEs

I am having a hard time trying to solve the following system of ODEs X'' = e^{2X} + e^{2Y} Y'' = e^{2Y} - 3 e^{2X} with initial conditions that mimic a linear ...
FM87's user avatar
  • 13
0 votes
0 answers

Explicit modified midpoint (Gragg smoothing)

In the "StifnessSwitching" method the default numerical scheme for the non-stiff solver is Explicit modified midpoint (Gragg smoothing) with a decreasing step size. I decided to study the ...
Van's user avatar
  • 13
4 votes
1 answer

FEM breaks because of Abs(f'(x))

I am trying to solve a 1d differential equation in Mathematica using the finite element method. I have successfully implemented the problem in a commercial software called COMSOL, but I like to use ...
Nils's user avatar
  • 71
10 votes
3 answers

Can NDSolve be initialized with a close solution?

I have a set of 4 first order ODE with 4 initial conditions to be met. It models a simple damped pendulum like the one described here. What changes is the damping term and I switched to first order ...
Meclassic's user avatar
  • 1,025