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I think substituting a in the definition of int, which is called by a is trouble, and what you really need is to make sure int isn't evaluated when z[t] isn't a number. The following seems to work, a …

The strength of noise σ = 20 seems large so that it can overwhelm the mean trend. Luckily Mathematica can give some analytical insights into this stochastic process. Clear[σ] proc = StratonovichProc …

I fixed the exp that @cvgmt noted, pulled τc and Ip out of NDSolve, and got rid of the extra initial conditions. τc[t] := (η L^3)/(8 c π^2) (n[t] (σe11 - σ111) V)^2; Ip[t] := 2.5 E^(-(t - 8)^2/(2 sd)) …

As I commented above, replacing 0 with time derivatives in the $w$ and $z$ equations times a small number $e$ lets NDSolve solve these equations. pts = 100; T = 0.2;(*Time integration -- the system e …

Sorry, I don't have time for a real answer right now, but here are some ideas that might help you or someone else come up with a robust solution. If you plot the function being solved inside sepICS y …

Simply increasing the MaxRecursion gives an answer without the NIntegrate::ncvb message: paverage = NIntegrate[p1, {t, 40, 40 + period}, MaxRecursion -> 100]/period (* {-311.506} *) BTW, looking …

I'm trying to plot how the Area of an ImplicitRegion defined by four (ugly) inequalities depends on parameters. It seems I need to Simplify first. a12 = \[Rho]/A; a13 = A \[Rho]; a21 = A \[Rho]; a23 …

You could use FindRoot to tweak the period (tmax) and x0 to get back to the starting point, with the other coordinates of the system fixed: map[H_,om_,x0_?NumericQ,y0_,ux0_,uy0_?NumericQ,tmin_,tmax_? …

The derivatives on the left hand side of your differential equation are multiplied by f[z], which is zero at z=1. This leads to the error messages Power::infy: Infinite expression 1/0. encountered. …

Can a time-based WhenEvent be triggered at the initial time within NDSolve? As a minimal example, a pulse is to be applied every integer time t, but NDSolve skips the initial pulse at t=0: sol = NDS …

Here's a way to numerically get the "curvy forks" of the pitchfork in the second example, using a pseudo-arclength continuation function I hacked together earlier. First, define TrackRootPAL from the …

Not an answer, but an extended comment. I am not sure there is a periodic orbit in your implementation of this system in Mathematica. Plot[Evaluate[x[1.303900184464743, 3.81159928041479][t] /. solp] …

Your code works for me with L = C1 = .001, it's just slow (326 seconds). Looking at the output shows why: Plot[u[t] /. sol, {t, 0, tmax}, PlotPoints -> 2000] Plot[u[t] /. sol, {t, tmax - 0.01, tmax} …

Following @user21's suggestion to look at this example in the docs, I made the following tweaks: vars = {p[t, x1, x2], t, {x1, x2}}; \[CapitalOmega] = Rectangle[{0, 0}, {3, 3}]; pars = <|"ModelForm" - …

If you run your first code for the same amount of time as the Poincare section, you'll see that they do agree (and that they're not particularly interesting parameter values): T = 2*Pi/1.2; sol = NDS …