# Tagged Questions

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

102 views

### Bessel-like equation problem with NDSolve

I am trying to solve the following nonlinear ODE, but Mathematica takes forever to give a result. Any idea why? ...
45 views

### Differential equation for a list with parameter dependent function

I am having a differential equation: y' = (1 - y) - f[y, mu] y; f is a hysteretic function that depends on y and on the derivative of y: ...
39 views

### Recursions where one definition depends on another. How to Block or have local variables?

I have been using Mathematica to solve a second order differential equation using the second order Verlet method. My code looks like: ...
212 views

210 views

### How to enforce a symmetric solution with FEM?

I'm solving the laplace equation in a domain with holes, and I need to compute the integral of the gradient on the boundary of these holes. For that I define a mesh and solve the laplace equation ...
34 views

### Replace variable with other variable containing a constant in differential expression [duplicate]

I have the following differential expression: ...
120 views

### Integration of Frenet-Serret differential equations [duplicate]

Are there programs available in Mathematica or other related sources where third order Frenet-Serret equations are numerically integrated to find coordinates in 3-space? Curvature/torsion given as ...
46 views

### implicit solution to PDE with strange return type

I want to solve the following PDE eqn = D[q[k, t], t] + \[Alpha] (1 - q[k, t]) D[q[k, t], k] == q[k, t] (q[k, t]-1) for $q(k,t)$. The solution that is returned ...
118 views

### Finite Difference - heat generation in a square (square within a square)

I am trying to develop a code that will allow me to solve the following problem. Lets say that I have a square block, inside that square block I have a smaller square box thats at a certain ...
171 views

### Differential equation in two variables

I have a system of second order differential equations, with two independent variables, which represents a trajectory. I tried solving this system using NDSolve and ...
43 views

### DSolve doesn't give an output for a system of ODEs

I'm trying to solve a system of four ODEs. However, DSolve doesn't give any output (no mistake either). ...
129 views

### What should I learn from DSolve working better with a named constant than a number in this case?

I have an equation $$\bigl(r''(\phi)r(\phi) - r'(\phi)^2\bigr)\bigl(b + r(\phi)\bigr) = r(\phi)\bigl(r'(\phi)^2 + r(\phi)^2\bigr)$$ Here $b$ and $r$ are lengths, and $\phi$ is an angle (in radians, so ...
165 views

### DSolve—different solutions for same set of equations using different symbols?

I happen to find that DSolve can give different solutions, even a different number of solutions, for a set of differential equations just by making a change in the ...
129 views

### How to creat mesh on the cube's surface?

Now I'm trying to solve a PDE by FEM, and I need creat the 2D mesh on the cube's surface, the figrue below shows my idea. Both the quadrilateral elements and triangle element are OK. I read the ...
101 views

How can we generalize the code previously introduced to solve the Fredholm equation of the second kind to the case of a system of Fredholm integral equations of the second kind? $$f_{1}(x)-\lambda_{... 1answer 172 views ### System of Four First Order Equations for Double Pendulum using RK-4 - Code Improvements I have spent quite a bit of time implementing the double pendulum equations at the bottom of this web site using Runge-Kutta-4. I am also quite aware of the built-in Runge-Kutta methods, but I need ... 2answers 224 views ### Solve numerical differential equations at t->Infinity I have a first order non-homogeneous system of differential equation (100+ equations, so no hope to solve them analytically, due to the Abel–Ruffini theorem). If I solve them using ... 1answer 105 views ### How many ODEs can NDSolve handle? I am trying to simulate a coupled system of N blocks and springs. I am using NDSolve. For ... 1answer 67 views ### Maximum step size as a scalar function on the domain In NDSolve when solving a system of ODEs, one can control the maximum time step for the whole domain with MaxStepSize. But there ... 1answer 49 views ### System of ODEs - NDSolve issues I am a self-taught beginner trying to use Mathematica for the first time. If you wouldn't mind, I would like to ask for help with the code I am working on as I keep running into multiple issues when ... 1answer 98 views ### Solution of differential equation using other differential equation [closed] I have a differential equation y'(t)+2a\sqrt{e+y(t)+1}=h-2a where e,h and a are constants with the terminal condition y(T)=0; T may be 10 or 12... etc. And x'(t)+(a/\sqrt{e+y(t)+1}) x(t)=-... 1answer 199 views ### Strange WhenEvent Behavior Bug introduced in 10.3 or earlier and persisting through 10.3.1 or later Given: ... 1answer 110 views ### DSolve with Piecewise Function in System of DEQs I have been messing around with this problem from MSE, which is given by:$$ \ddot{x} = \begin{cases} -x + c\cdot \operatorname{sgn}(x)& |x| > c\\ 0 & |x|\leq c \end{cases}  where $c &... 1answer 237 views ### Solve motion from Hamilton's equations I have a system of four coordinates and four momenta (conjugates of coordinates). I have a metric tensor$g_{ik}$and I know the Hamiltonian:$H(p,q,t)=\frac{1}{2}g^{ik}(q)p_ip_k$For my current ... 1answer 88 views ### Solving an equation and ODE simultaneously [closed] I have a differential equation like$y'+a*y+b=0$. I have to find the value of$u=c*y+d$. These are the simplified form of the ODE and equation. Also, I have to plot$y$and$u$together. 1answer 200 views ### Problem with a plot for 1D wave equation solution using NDSolve [closed] I can't properly use Manipulate for my solution of a wave equation. Can anyone help me? I have the wave equation in the form: ... 1answer 94 views ### Dsolve and Differential Equation for botnet defence I am currently using Mathematica to solve$\frac{\mathrm{d}x(t) }{\mathrm{d} t} = cv_{H} (1-x) + \beta x(1-x) - (\gamma_{min} - v_{D}(\gamma_{max} - \gamma_{min}))x$with$ x(0) = 0$. In the ... 0answers 92 views ### unhandled win32 exception in WolframKernel.exe in DSolve of non-linear ODE in one variable Bug persisting through 10.4. (windows 7, 64 bit) Installed 10.3.1 and started to run some old ode's. in V 9, this ode used to return unsolved, which is ok, but in 10.3.1 now the kernel crashes. ... 2answers 127 views ### inspecting step size and order of$\tt NDSolve\$

I am trying to collect information about what step sizes and what orders is using NDSolve internally. I tried wrapping it into a ...