Non-linear Definition and 318 Threads

Hello everyone, A few days ago I stumbled across the formula for the energy of a moving breather for the Sine-Gordon equation $$\Box^2 \phi = -Sin(\phi) $$ The energy in general is given by (c=1) $$ E = \int_{-\infty}^{\infty} \frac {1} {2} ((\frac {\partial \phi} {\partial x})^2+ (\frac...

a) We can use reduction of order $$p=y'\tag{1}$$ $$p'=y''\tag{2}$$ The DE becomes $$p'+p^2=0\tag{3}$$ $$\frac{1}{p^2}p'=-1\tag{4}$$ This last step contains the assumption that ##p^2=y'^2\neq 0##. $$-\left (\frac{1}{p(x)}-\frac{1}{p(x_i)}\right )=-(x-x_i)\tag{5}$$...

Question: Solution first part: Have I done it right? I don't know how to begin with second part since the dielectric is non-lineair, and most formulas like $$ D=\epsilon E$$ and $$P= \epsilon_0 \xhi_e E$$, only apply for lineair dielectrics. What to do?

Trampolines are in effect coupled springs, with the mat being the much softer spring generally. E.g. On my Acon, when jumping about 1 meter, there is a max cone of depression about 60 cm deep and 1 meter across (1 meter point has a depression of only about 10 cm) At this same point the 160 or...

For a nonconservative force, What would be the dissipative function for a force f=-bvⁿ in Lagrangian (Where v is the velocity) [#qoute for a nonconservative force f=-bv The dissipative function is D=-(1/2)bv² ] Since ##f=\frac{\partial D}{\partial \dot x}## so the dissipative function should...

Suppose there is an exam of maths, for a particular service, whose syllabus is of Bachelor of Science: Maths level, i.e. the syllabus includes (exhaustively) Linear Algebra, Abstract Algebra, Calculus, Vector Calculus, Real Analysis, Complex Analysis, Ordinary Differential Equations, Partial...

The top most 2nd order non-linear DE is the one that has to be solved. Below is the solution. This problem is from Morin's Classical Mechanics. May I know how he could guess that r = Agt^2? Firstly, why must g tilda be a variable within r? I do not understand what he meant by 'parameter'...

I have an experimantally obtained time series: n_test(t) with about 5500 data points. Now I assume that this n_test(t) should follow the following equation: n(t) = n_max - (n_max - n_start)*exp(-t/tau). How can I find the values for n_start, n_max and tau so as to find the best fit to the...

In the famous book, Gravitation, by Misner, Thorne and Wheeler, it talks about the stress-energy tensor of a swarm of particles (p.138). The total stress-energy is summed up from all categories of particles. Is summation meaningful in the non-linear theory of Einstein gravitation? Thanks.

Many circuit analysis techniques only apply to linear circuits. I don’t quite understand how to distinguish between linear and non-linear circuits. I understand the mathematical concept of linearity. I understand why components like resistors, capacitors and inductors are linear. I don’t quite...

Hi, Could you please have a look on the attachment? Question 1: Why is this differential equation non-linear? Is it u=\overset{\cdot }{m} which makes it non-linear? I think one can consider x_{3} , k, and g to be constants. If it is really u=\overset{\cdot }{m} which makes it non-linear then...

Hi, I was working on a predictive linear regression model and was hoping to obtain some bounds to represent the uncertainty present in the model. Question: I suppose this boils down into two separate components: 1. What is a good measure of uncertainty from a linear regression model? MSE, or...

I have a matrix M which in block form is defined as follows: \begin{pmatrix} A (\equiv I + 3\alpha J) & B (\equiv -\alpha J) \\ I & 0 \end{pmatrix} where J is an n-by-n complex matrix, I is the identity and \alpha \in (0,1] is a parameter. The problem is to determine whether the eigenvalues of...

Hello, I am trying to compute some non-linear equations with pseudospectral/collocation methods. Basically I am expanding the solution as $$ y(x)=\sum_{n=0}^{N-1} a_n T_n(x), $$ Being the basis an Chebyshev polynomial with the mapping x in [0,inf]. Then we put this into a general...

Say you have the set of coupled, non-linear ODEs as derived in this thread, it has two unknowns ##N(t)## and ##\theta(t)##: $$ N - mg = - m\frac{L}{2}\left(\dot{\theta}^2\cos(\theta) + \ddot{\theta}\sin(\theta)\right)$$ $$ \frac{L}{2}N\sin(\theta) = \frac{1}{12}ml^2\ddot{\theta}$$ What freedom...

I often hear about non-linear or chaos having order, and have difficulty grasping the concept. For example, you have weather disorder, how can it bring order? or you have Covid chaos, how can it bring order? Can you give some examples of the concept? What is fact, myth, and misconception...

My History -------------- I attended Oregon State U. and majored 3 years in Electrical Engineering. Then I switched to a Math major for my final years and graduated with a B.S. in Math (1967). Developed several Apps for Engineers & Scientists. My first job was with Lockheed Aircraft Co...

If we have the following relations between x, y, and z: M_{xy}=\frac{2xy}{x+y} M_{xz}=\frac{2xz}{x+z} M_{yz}=\frac{2yz}{y+z} where M_{xy}, M_{xz}, and M_{yz} are known constants, what technique can be used to determine the values of x, y, and z?

I seem to remember from my school days that Tension Force can only be linear. Is this true? In 1 (in the graphic) the tension will follow the line of the rope In 2 there is an unbendable, unbreakable, steel cable formed into an arch. a ] In 3 which direction will the Tension be? b ] In 3 if...

Hello, I'm working on a project controlling a UAV (quadcopter) I'm trying to understand non-linear PID controllers. I know that a linear PID is given by: and a non-linear PID the konstant terms are replaced with functions My question is: how to i find these function and tune the paremeters, i...

I honestly don't know how to quite even begin this problem. Looking at Fig 3-2, the slopes of the graphs are 1/R, and hence where the slopes are 0, we have infinite resistance, in which case current wouldn't flow through that resistor and hence simplify the circuit. So I was trying to find...

I need to apply, with CAMB code, a correction on ##\sigma_{8}## between linear and non-linear regime to keep it fixed (I make change the values of cosmological parameters at each iteration). I have to compute ##\sigma_{8}## from the ##P_{k}## and found the following relation (I put also the text...

i am doing research to make criteria by which i can identify easily linear and non-linear and also identify its singular or not by doing simple test.please help me in this regard.

I want to solve $\d{y}{x}=\frac{3*(2x-7y)+6}{2*(2x-7y)-3}.$ I don't know its step by step solution. But using some trick of solving ordinary differential equation (which I saw on the Internet), I got the following solution:- $-\frac{17}{21}*(3x-2y)+ln(119y-34x-48)=C$. Now how to solve this...

What is the method to design a Non - Telescopic, Non - Linear, conical compression spring from a Force - Deflection characteristics

Homework Statement equations above are descriptive of a system with two configuration variables, q1 and q2. inputs are tau1 and tau2. d and c values are given. the question is about conversion of above equations to a state-space equation where the state-variables are x1 = q1_dot, x2 = q1_2dot...

If I calculate the time period of a non linear pendulum using elliptical integral equation, then how can I find out the angular displacement.

I've finally worked out a derivation of the Lorentz transformation that doesn't use the now out of favor i^2=-1, but it still has one weak spot: it assumes that the transformation is linear. It seems quite reasonable to me that it would be linear since it has to graph straight lines on to...

Homework Statement z\frac{d^2z}{dw^2}+\left(\frac{dz}{dw}\right)^2+\frac{\left(2w^2-1\right)}{w^3}z\frac{dz}{dw}+\frac{z^2}{2w^4}=0 (a) Use z=\sqrt y to linearize the equation. (b) Use t=\frac{1}{w} to make singularities regular. (c) Solve the equation. (d) Is the last equation obtained a...

Hello everyone, I've always had this question in my mind: Can we convert the non-linear function into a system of linear functions? I don't know if this is actually something exist in math (I searched a little bit to be honest), but I'm really interested in this question because it would make...

Hi, Im wondering if / how commercial FEA codes take into account additional unbalance forces due to the off-axis displacement of masses. For instance, if I am modeling a jeffcott rotor with an unbalance, I would traditionally represent this unbalance with a force that increases with speed^2...

Homework Statement ##\frac{d^2y}{dx^2}=2xy\frac{dy}{dx}##Homework Equations This is second order non-linear pde of the 'form' ## f(y'',y',y,x) ## . I have read that there are 2 simplified versions of a second order non-linear pde that can be solved easily and these are 1) when there is no y...

The question is prompted by a claim raised in another thread that "There is good reason (theoretically) to believe that linearity fails at high enough energies." I've put this with an A prefix because it is going to be about some damned difficult maths, I know. But please try to avoid the...

I'm working on a physics "potential" problem and trying to create an alternate function to describe the potential energy. I'm having trouble figuring out how to solve a nonlinear ODE, or even a limiting boundary for minimizing a drop off shape function. I was able to reduce my problem to the...

Hi, I tried to solve the following in Wolfram alpha: y''' + (1-x^2)y=0 y(0)=0 y'(0)=0 y''(0)=0 however, I got answer which cannot be reproduced (even at wolfram pages). I have tried ODE45 in MATLAB, but it only gives a plot. Is there any way to solve this analytically or numerically to give...

Could the space (air gap) between two DC charged parallel plates be considered to be a "non-linear" medium with respect to an EMF radiated by a coil contained within that space?

Homework Statement I have found a differential equation that models a non-linear pendulum with air resistance, and now I have data. I've looked at the following site for guidance on how to analyse the data. It compares the motion of a damped spring, and compares it to the motion of a damped...

Homework Statement I need to come up with an equation that would model the motion of a non-linear pendulum with air resistance. [/B]Homework Equations Fc=mgsintheta Fdrag=(1/2)p(v^2)CA The Attempt at a Solution I started with mgsintheta-(1/2)p(v^2)CA=ma After substituting v=r*omega and...

Hi, I have in a previous thread discussed the case where: \begin{equation} TT' = T'T \end{equation} and someone, said that this was a case of non-linear operators. Evidently, they commute, so their commutator is zero and therefore they can be measured at the same time. What makes them however...

So the slope is of course a ratio of the change in y-coordinates to the change in x-coordinates. This is easy to see with a linear equation. I just came across a cool math simulator ( https://phet.colorado.edu/sims/equation-grapher/equation-grapher_en.html), and I left the first value (ax^2)...

Suppose ##A## is a linear operator ##V\to V## and ##\mathbf{x} \in V##. We define a non-linear operator ##\langle A \rangle## as $$\langle A \rangle\mathbf{x} := <\mathbf{x}, A\mathbf{x}>\mathbf{x}$$ Can we say ## \langle A \rangle A = A\langle A \rangle ##? What about ## \langle A \rangle B =...

1. Problem Recall that we defined linear equations as those whose solutions can be superposed to find more solutions. Which of the following differential/integral equations are linear equations for the function u(x,t)? Below, a and b are constants, c is the speed of light, and f(x,t) is an...

I have a little question. I want to know if there is a process in which I can find equilibrium solutions to some system of difference equations. For example, if I have something crazy like $$\begin{cases} x[n+1]=(x[n])^2y[n]+z[n]e^{-ax[n]} \\ y[n+1]= z[n]x[n]+x[n+1]y[n+1]\\ z[n+1]=...

Hi, Out of interest, today I was mucking around with a 160W LED, 240V, 50hz, outdoor light. I looked at the Power Factor (it was 0.96) and the THD was 14.something %. I then wondered what would happen if I put a capacitor in parallel with the light. It was a three phase 90uF cap, so since they...

Homework Statement I'd like to understand Drag Force better; but school always ignores it. Thus, I'm asking this purely out of obssession. I'm picturing a scenario where a non-constant force is pushing an object horizontally, ignoring friction. But, I'd like to understand how Drag Force...

I have a physics project at university, we designed an experiment to measure the effectiveness of Poiseuilles law in a 'quasi non-steady state'. Poiseuilles law, simply being the measurement of the flow rate of a fluid in a pipe, holding only under steady state though. So by quasi steady state I...

I have some experience with non-linear least squares curve fitting. For instance, if I want to fit a Gaussian curve to a set of data, I would use a non-linear least squares technique. A "model" matrix is implemented and combined with the observed data. The solution is found by applying well...

Hi, The problem is to solve: dy/dx = −[2x + ln(y)]*(y/x) Attempt: I have tried to see if it is exact, I found it not to be, I can't easily find a function to multiply by to make it exact either (unless I am missing something obvious). It clearly isn't seperable, nor is it homogenous (I know...

Can someone check my work here? Both ##f=f(x)## and ##y=y(x)##. $$f'y'+\frac{fy''}{1+y'^2}=0\implies\\ \frac{y''}{y'(1+y'^2)}=-\frac{f'}{f}\\ \frac{y''}{y'(1+y'^2)}=-\ln(f)$$ Now let ##v=y'##, which implies $$...

Hi guys! I study Electrical Engineering and, don't-know-why, I don't know anything about state space. Now I'm working on a project where I have a non-linear system. The first task in the project is to separate the linear and the non-linear part of this system, and then obtain the state space...