Short-answer question on characteristics of p.d.e

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In summary, the question asks for what expressions are constant along the equations's characteristics, and the answer is that u=sqrt(x) and u=sqrt(-2t) are constant. It may be better to state the solution function u(x,t) in implicit form instead of solving it explicitly for u.
  • #1
Maximtopsecret
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Homework Statement


ut − 2ux =1/ u;
what expressions are constant along the equations's characteristics?

Homework Equations


3. The Attempt at a Solution [/B]
Am I right?
dt=dx/(-2)=du/(-1/u), -2t=x=u2;
u=sqrt(x); u=sqrt(-2t) are constant.
 
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  • #2
I think that they may want a slightly more general answer. Have you quoted the question precisely as it was stated?
 
  • #3
MarcusAgrippa said:
I think that they may want a slightly more general answer. Have you quoted the question precisely as it was stated?
Oh yes, the question is stated just like there...
 
  • #4
Maximtopsecret said:
Oh yes, the question is stated just like there...

Then, apart from the fact that you have ignored the second branch of the square root function, your answer is correct. It may be better to quote the solution function u(x,t) in implicit form rather than to solve it explicitly for u. That way you include both branches of the square root function.
 

1. What is a partial differential equation (PDE)?

A partial differential equation is a mathematical equation that involves multiple independent variables and their partial derivatives. It is used to model and describe physical phenomena in various fields such as physics, engineering, and economics.

2. What are the characteristics of a PDE?

There are several characteristics of a PDE, including linearity, order, and boundary conditions. Linearity means that the equation is linear in its dependent variables and their derivatives. The order of a PDE is determined by the highest derivative present in the equation. Boundary conditions specify the values of the solution at the boundaries of the domain.

3. What is the difference between an ordinary differential equation (ODE) and a PDE?

The main difference between an ODE and a PDE is that an ODE involves only one independent variable, while a PDE involves multiple independent variables. This means that the solution of a PDE is a function of more than one variable, whereas the solution of an ODE is a function of a single variable.

4. What are some common examples of PDEs?

Some common examples of PDEs include the heat equation, wave equation, Laplace equation, and diffusion equation. These equations are used to model various physical phenomena such as heat transfer, wave propagation, and diffusion processes.

5. How are PDEs solved?

There are various methods for solving PDEs, including separation of variables, method of characteristics, and numerical methods such as finite difference and finite element methods. The choice of method depends on the specific characteristics of the PDE and the problem being solved.

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