Non-linear ODE with IV problem

In summary, the conversation discusses solving a piecewise ODE that is non-linear and of order one. The solution involves solving two parts separately and results in a single solution defined in two pieces. The conversation also mentions the importance of understanding the conditions and initial conditions for the solution.
  • #1
mistereko
26
0

Homework Statement



I just need to know how to start this. I've never seen a piece wise ODE before and I don't really know where to start to be honest. I know it's non-linear and it's of order one.

dy/dx = (1/3)y - 3, y > 0 and dy/dx = -(1/3)y - 3 ≤ 0. y(0) = 1 with y(x) [itex]\in[/itex] C0 [0,[itex]\infty[/itex])

I'm trying to find the non-trivial solution.

Homework Equations





The Attempt at a Solution


 
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  • #2
Just solve the two parts separately.
 
  • #3
Thanks very much. That should be ok. :)
 
  • #4
mistereko said:
Thanks very much. That should be ok. :)

So, will I have two solutions in the end?
 
  • #5
mistereko said:
So, will I have two solutions in the end?

You'll have a single solution defined in two pieces. Are you sure that the pieces are y>0 and y<=0? Not x?
 
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  • #6
No. You will have a single solution- a single function given by one formula for x< 0 and second formula for x> 0- a "piecewise function".

I clearly type too slowly!
 
Last edited by a moderator:
  • #7
Thanks guys.
 
  • #8
It's definitely a linear ODE right?
 
  • #9
mistereko said:

Homework Statement



I just need to know how to start this. I've never seen a piece wise ODE before and I don't really know where to start to be honest. I know it's non-linear and it's of order one.

dy/dx = (1/3)y - 3, y > 0 and dy/dx = -(1/3)y - 3 ≤ 0. y(0) = 1 with y(x) [itex]\in[/itex] C0 [0,[itex]\infty[/itex])

I'm trying to find the non-trivial solution.

Homework Equations





The Attempt at a Solution


It is important to know if you mean that
[tex] y' = \frac{y}{3} - 3, \; y > 0, \text{ and } y' = -\frac{y}{3} - 3, \;
y \leq 0, [/tex]
or
[tex] y' = \frac{y}{3} - 3, \; x > 0, \text{ and } y' = -\frac{y}{3} -3, \; x \leq 0.[/tex]
Both systems have [itex]C^0[/itex] solutions; one of them has [itex]C^1[/itex] solutions, but the other does not (except for one very particular choice of initial conditions).

RGV
 
  • #10
Ray Vickson said:
It is important to know if you mean that
[tex] y' = \frac{y}{3} - 3, \; y > 0, \text{ and } y' = -\frac{y}{3} - 3, \;
y \leq 0, [/tex]
or
[tex] y' = \frac{y}{3} - 3, \; x > 0, \text{ and } y' = -\frac{y}{3} -3, \; x \leq 0.[/tex]
Both systems have [itex]C^0[/itex] solutions; one of them has [itex]C^1[/itex] solutions, but the other does not (except for one very particular choice of initial conditions).

RGV

The first one you wrote. Cheers.
 

1. What is a non-linear ODE with IV problem?

A non-linear ODE with IV (initial value) problem is a type of differential equation that involves a non-linear relationship between the dependent variable and its derivatives, along with a set of initial conditions. These initial conditions specify the values of the dependent variable and its derivatives at a given point in the independent variable.

2. How does a non-linear ODE with IV problem differ from a linear ODE?

A linear ODE (ordinary differential equation) is one where the dependent variable and its derivatives have a linear relationship. This means that the dependent variable and its derivatives appear only to the first power. In contrast, a non-linear ODE with IV problem has a non-linear relationship between the dependent variable and its derivatives, meaning they can appear to higher powers.

3. What are some real-world applications of non-linear ODE with IV problems?

Non-linear ODE with IV problems have a wide range of applications in various fields, including physics, engineering, economics, and biology. Some examples include modeling population growth, predicting the spread of diseases, analyzing chemical reactions, and understanding the behavior of complex systems such as weather patterns.

4. How are non-linear ODE with IV problems solved?

Unlike linear ODEs, there is no general method for solving non-linear ODE with IV problems. However, there are various techniques and numerical methods that can be used to approximate solutions, such as the Euler method, Runge-Kutta methods, and series solutions.

5. What are the challenges of solving non-linear ODE with IV problems?

One of the main challenges of solving non-linear ODE with IV problems is that they do not have a general solution, making it difficult to find an exact solution. Additionally, non-linear ODEs often have complex and unpredictable behavior, making it challenging to analyze and interpret their solutions. This requires advanced mathematical techniques and computational tools to approximate solutions and understand their behavior.

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