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Questions on the symbolic (DSolve, DifferentialRoot) and numerical (NDSolve) solutions of differential equations in Mathematica.

3
votes
Look at https://reference.wolfram.com/language/ref/NDSolveValue.html in Possible issues/Multiple Solutions. They are indeed saying that NDSolveValue can't make it. There are two possible differential …
answered Nov 23 '18 by J.A
0
votes
1answer
I just started to use Mathematica. I don't manage to use NDSolve. For example, when I write s2 = NDSolve[{y[x]^2 = x, y[1] == 1}, y, {x, 0, 30}] Plot[Evaluate[y[x] /. s2], {x, 1, 2}] It doesn …
asked May 9 '18 by J.A
0
votes
0answers
I have a question please. I have an issue with my code while trying to solve an equation. Here it is : sol = Block[{\[Epsilon] = $MachineEpsilon}, NDSolve[{Div[(f[x])*(1 - f[x])*Grad[(-2 f[x] + 4*f[x …
asked May 14 '18 by J.A
0
votes
1answer
I'm getting crazy with this Manipulate : Clear[l, L, nc, phic, tauC, tauG, tauS, phi0, Vinitphi, Vphi0, nL0, \ V, Vphi, VinitR, VinitR0, dV, V0, Vphi0] VinitR0 = 0 L = 6000 nL0 = 1 phi0 = 0.4 mode …
asked Jun 14 by J.A
1
vote
1answer
I have an equation that I solve : sol = NDSolve[{ Div[(1 - f[x]) Grad[f[x], {x, y}, "Polar"], {x, y}, "Polar"] == -(1 - f[x]) f[x] (f[x] - 0.8), f[1] == 0.7, f'[0.00001] == 0.0001}, f, {x, 0.000 …
asked Jun 11 '18 by J.A
1
vote
0answers
I'm working on differential equations and I first used a potential without Piecewise. But given that I wanted to constrain the values between 0 and 1, I started to use Piecewise in the potential, maki …
asked May 22 '18 by J.A
0
votes
0answers
I'm trying to solve the following differential equation with some specific conditions NDSolve[{2 V[X] - 2 X Derivative[1][V][X] - X^2 V[X] Derivative[1][V][X] + 4 X^3 V[X] Derivative[1][V][X] - X …
asked Nov 5 '18 by J.A
1
vote
1answer
Is it possible to make a parametric ItoProcess ? I'd like to write that equation : V0 = 1 a = 0.1 i0[Vt0_] = ItoProcess[\[DifferentialD]V[t] == a*Plus[UnitStep[V0 - V[t]] V[ t]*\[DifferentialD]t …
asked Apr 11 by J.A
0
votes
2answers
I'd like to plot the maximum of a curve in function of a parameter. Meaning I looking for maxima that depend on a parameter. Here is what I tried to do but FindMaximum is not parametric, so it did no …
asked May 9 by J.A
0
votes
So I eventually used Table, which allows a "manual parametrization" : a = 1/2 F[x_, y_, z_] = (1 + a*y)*x^2*z^2 - b*x*y mux[x, y, z] = D[F[x, y, z], x] muy[x, y, z] = D[F[x, y, z], y] muz[x, y, z] = …
answered May 10 by J.A
1
vote
0answers
I'm trying to write a stochastic differential equation, using ParametricNDSolve and WhenEvents : s = ParametricNDSolve[{V'[t] == Piecewise[{{(a + mu[t])*V[t], V[t] < V0}, {(a + mu[t])*V[t]^(2/3 …
asked Apr 11 by J.A
0
votes
0answers
So I have a quite complicated ParametricNDSolve : taustart=5; epsilon=0.0001; v=600; L=1000; D0=9*10^4; nR=1; sol = ParametricNDSolve[ {R'[ t] == (D0 E^(-((L - t v)^2/(4 D0 t))) (L + t v))/( …
asked Jul 24 by J.A
0
votes
1answer
I would like to implement a sort of Euler explicit manually. I have this code alpha=1 a = 9/4 SOL[R_] = NDSolveValue[{-alpha * (-2 + 12*a*f[x]^2)*Laplacian[f[x], {x, y, z}, "Spherical"] == (Ma …
asked Jun 13 '18 by J.A
1
vote
1answer
I'm trying to solve the heat/diffusion equation in 3d in spherical symmetry $\partial_t f=D\Delta f$. I wrote : DSolve[{D[f[x, t], t] == Laplacian[f[x, t], {x, y, z}, "Spherical"],f[R,t]==C0,f[Infini …
asked Jan 29 by J.A
0
votes
1answer
I have some data : data={{9., 16.8895}, {12., 17.3404}, {15., 17.1633}, {18., 19.3417}, {21., 17.9899}, {24., 19.9677}, {27., 19.4362}, {30., 20.6519}, {33., 19.4591}, {36., 20.6855}, {39., 20.1952 …
asked Apr 12 by J.A

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