Questions tagged [discontinuity]
Tag for issues caused by discontinuity (e.g. Boole, Piecewise, UnitStep, If, etc) in arithmetic function.
46
questions
5
votes
1answer
99 views
Problem with using NDSolve on wave PDE on string
I am trying to verify my hand solution for wave PDE in 1D, on a string. The solution I get from NDSolve does not match the analytical solution.
This is a string, ...
3
votes
1answer
64 views
Piecewise function not evaluating in NDSolve
Perhaps it's something obvious, but why does this simple piecewise function (as well as other conditionals) not evaluate in NDSolve:
...
6
votes
2answers
162 views
Ndsolve problem with Sign (friction)
In a very simple model I consider the motion of a body with frictional force.
...
6
votes
3answers
503 views
How to set interface conditions for optical waveguide in NDEigensystem?
I have been working on waveguide mode analysis using FEM in Mathematica for a week, but I haven't succeeded until now.
The optical fiber-like waveguide is featured with different refractive index in ...
0
votes
1answer
75 views
NDSolve gives unexpected results when using the method of lines
I've been trying to solve the following PDE using the NDSolve function but it seems something is not working properly. The PDE is a the heat equation on polar coordinates and assuming angular simmetry:...
1
vote
0answers
30 views
Discontinuities in taking the roots of a complex function
I have the following functions e1, e2, and e3 which consists of the functions ...
5
votes
1answer
96 views
NDSolve with piecewise boundary conditions
I am trying to solve two simultaneous partial differential equation for $P[x,t]$ and $V[x,t]$. I have a piecewise boundary condition for $V[L,t]$. When using that piecewise condition, I get the error
...
4
votes
2answers
147 views
Heat equation with variable conductivity
Let us consider the (very simple) problem
$\qquad \partial_x[k(x)\,\partial_xu]=0,\quad x\in [0,1]$
$\qquad u(0)=0,\ u(1)=1,$ with $l\in(0,1)$
$\qquad k(x)=\left\{\begin{array}{l}k_1^{},x<l\\k_2^...
5
votes
0answers
56 views
Evaluation of Mod of InterpolatingFunction prevents discontinuity processing by Plot
While trying out @MichaelSeifert's answer to Eliminating Discontinuities When Using Mod with NDSolve and Plot for Oscillators,
I came across this odd behavior. Depending on how an ...
2
votes
1answer
60 views
Eliminating Discontinuities When Using Mod with NDSolve and Plot for Oscillators
I have found similar questions to mine, but dealing with piecewise and parametric plots instead and unfortunately the answers don't seem to extend to my case.
I have a solution from ...
0
votes
1answer
61 views
ContourPlot showing breaks in contours
I'm trying find graphically the solutions of the intersection of the following functions.
...
0
votes
1answer
65 views
Finding the discontinuities of a function
I have a list of data and I want to find the discontinuities in the plot of them but I don't want to use interpolation because it is not that exact that it should be. is there any other way?
The ...
0
votes
1answer
59 views
Defining a function with a point of finite discontinuity [closed]
I wrote the code for the function $T$ defined on $[0,1]$ by $T(x)=\frac{x+2}{3}$ if $x\neq\frac{1}{2}$ and $T(\frac{1}{2})=1$ as follows.
...
0
votes
2answers
73 views
How to plot 3D discontinuous iterative plot?
I am having troubles with plotting this set of data
triples={{0, 1, 1}, {9/50, 4/5, 1}}, {{9/50, 4/5, 1}, {3/8, 4/5, 1}}, {{3/8, 58333/100000, 1}, {3/4, 16667/100000, 1}}, {{3/4, 0, 1}, {1, 0, ...
0
votes
0answers
45 views
How to get rid of the discontinuities in the plots and animation?
Trying to plot the angles for a double pendulum against each other such that they stay within the bounds of -Pi to Pi. The NDSolve solves the equations such that if a pendulum does a full loop the ...
6
votes
2answers
100 views
Finding a removable singularity
I have more complex functions than this, but say I just have:
f[x_]:=(x-a)/(x-2)
The function is not defined for x==2. I ...
1
vote
2answers
96 views
Solving an ODE with a sign/step function which depends on the time derivative
I'm trying to solve a set of ODEs with a Heaviside step function which depends on the sign of the derivative of the function.
This is a simplifying example of what I'm trying to do
...
3
votes
2answers
97 views
Using NDSolve with conditional expression
I am trying to solve the 2nd order ODE for a harmonic oscillator under the influence of a harmonic restoring force, a sliding friction force, and a static friction force. My equations are below:
$$ x'...
3
votes
1answer
81 views
WhenEvent - energy conservation not valid [closed]
I would like to simulate the following conservative system, with purely elastic impacts (coefficient of restitution is 1). Applying the WhenEvents the energy of the system is not conserved.
How can I ...
6
votes
1answer
272 views
The rectangular region composed of two triangular regions contains a pde connecting the bc of the first and the second kind
I'm going to solve the Laplacian equation of the electrostatic field, which consists of two triangular regions, a rectangular region, a square, and on the intersection of the two regions of $$y=x$$, ...
2
votes
1answer
33 views
Summations with power of DiscreteDelta
Expression
Sum[DiscreteDelta[a - 1]^2, {a, -∞, ∞}]
evaluates to 1, as expected, but
Sum[DiscreteDelta[a - b]^2, {a, -∞, ∞}]
does not converge, according to ...
2
votes
0answers
47 views
How to express continuity assumption for Integrate?
I am wondering if it is possible, and how if so, to express function continuity in the assumptions for the definite form of Integrate.
First of all, while
...
4
votes
2answers
256 views
Problem in sharpness of Heaviside Function
The Heaviside function is not sharp, Do not know why?
...
1
vote
0answers
65 views
Saturation function in Mathematica [duplicate]
In Simulink, there is a function called Saturation:
Is there function like that in Mathematica? If yes, what is it called?
0
votes
1answer
122 views
Piecewise continuation of a discrete function on an area
I have a discrete function (finite set of values) defined on an area $\Omega$ in $R^2$. Each value of the function is defined on a subarea $\Omega_i$(triangle in my case). These triangles account for ...
2
votes
1answer
200 views
NDSolve cannot do a discontinuity replacement for event surfaces that depend only on time
I'm trying to solve a system of DAEs with discrete conditions:
...
1
vote
0answers
164 views
NDSolve unable to handle discontinuities
I'm trying to solve a set of ordinary non-linear differential equations but running into issues. Specifically, after supplying Mathematica the below definitions and evaluating the ...
1
vote
2answers
143 views
4
votes
1answer
194 views
Options of WhenEvent
I'm using NDSolve and WhenEvent to simulate building heating systems and their discontinuous operation. Here is a simplified example.
The idea is quite simple. I have the following WhenEvents:
<...
2
votes
1answer
257 views
Force derivative of piecewise function at boundary points to be one-sided derivative
I've defined a smooth step function given as
f[x_] = Piecewise[{
{y0, x<x0-dx/2},
{y0+1/2(y1-y0)(1-Cos[Pi*x/dx]), x<x0+dx/2},
{y0, True}
}];
...
6
votes
2answers
531 views
Solving wave equation with singular initial conditions
I am trying to compute the solution to the wave equation using NDSolveValue and singular initial displacement (continuous, but not differentiable in a point). I ...
3
votes
0answers
97 views
NDSolve produces different solutions for the same set of equations [duplicate]
I've tried to simulate simple mechanical system - mass which is pulled on a spring. The code You can find below. Unfortunately, I can't get correct results. But, what has surprised me more, is that ...
1
vote
1answer
782 views
A discontinuity in a plot of a continuous function
I plot a continuous, though not a smooth function:
Plot[If[a >= 0.5, 0, Sqrt[0.5 - a]], {a, -1, 1}, PlotRange -> All]
which returns the following
One can ...
2
votes
1answer
163 views
Piecewise causes ndnum warning in NDSolve
Bug introduced in 8.0.4 or earlier.
I try to solve the heat transfer equation with boundary condition that depends on time:
...
7
votes
1answer
584 views
Free Convective Heat Transfer of Non-Newtonian Power Law Fluids from a Vertical Plate
I am trying to solve a set of PDEs mentioned in this paper with NDSolve but facing quite a few issues.
The PDE system is:
...
7
votes
2answers
275 views
NDSolve with Piecewise solving BVP gives warning bvdisc [duplicate]
Backslide introduced in 9.0, persisting through 11.0.1
I try to solve a boundary value problem of coupled ODEs. For reference, when I solve this set of equations it works without any problems:
...
10
votes
3answers
660 views
Position of discontinuous coefficient influences the solution of PDE
This issue is raised in the discussion under this post about heat flux continuity and I think it's better to start a new question to state it in a clearer way. Just consider the following example:
<...
5
votes
3answers
292 views
How to complete function which is not defined for all interval
I have a function testF22 like this
...
1
vote
2answers
186 views
5
votes
1answer
203 views
Discontinuous boundary condition distorts in the numeric solution
Here I want to simulate a physical model that I have used a set of differential equations.
My coefficients and parameters:
...
11
votes
1answer
1k views
NDSolveValue - Heat flux continuity
I'm having some problems with NDSolve and the problem of conduction of heat. Specifically I'm having problems with the continuity of heat flux. First, let me ...
4
votes
2answers
384 views
Can't use my own discontinuous coefficient within NDSolve
I want to evaluate the pendulum's motion with changing equilibrium state given by eqilValue[t]:
...
7
votes
1answer
3k views
NDSolve and Piecewise functions [duplicate]
Backslide introduced in 9.0, persisting through 11.0.1
I want to clarify upfront, This is not a please help me get the answer to my homework question. I know what I need to do I just do not know how ...
10
votes
3answers
2k views
Can NDSolve handle discontinuous data?
Backslide introduced in 9.0, persisting through 11.0.1
It is possible to numerically solve a differential equation if not-smooth data are involved?
For example the following instruction return the ...
32
votes
3answers
4k views
Plot a piecewise function with black and white disks marking discontinuities
Let's say I'd like to plot Sign[x + 0.5]:
Plot[Sign[x + 0.5], {x, -1, 1}]
Mathematica will give this:
This plot does not ...
5
votes
4answers
2k views
NDSolve with Piecewise gives the incorrect answer randomly
Bug introduced in 9.0 and fixed in 11.1
NDSolve in Mathematica 9.0.0 (MacOS) is behaving strangely with a piecewise right hand side. The following code (a ...
