Laplace Transforms to solve non IVPs?

In summary, the conversation discusses using a Laplace transform to solve a differential equation and the difference between initial value problems and boundary value problems. Some argue that Laplace transforms are overrated and other methods, such as variation of parameters, could be used to solve the given problem. However, some believe that Laplace transforms have their own unique benefits. The possibility of using Laplace transforms to solve endpoint value problems is also mentioned.
  • #1
Alex6200
75
0
Is it possible to use a laplace transform to solve a problem like

x' + x = T

where x is a function of T and x(0) = 5 and x(4) = 7

Or can you only solve initial value problems?
 
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  • #2
Isn't that already an initial value problem? You are given x(0). Yes you can use the Laplace transform to solve it.
 
  • #3
No, that is not an initial value problem. Since it is a second order differential equation, an "initial value problem" would have x and x' given at the same value of t. Since you are given x at two different values of t, that is a "boundary value problem" which is significantly harder than an initial value problem.

I've always felt that "Laplace transform" was over rated. It gives a very "mechanical" way of solving problems that could be done in other ways. A problem like the one given here, to me, cries out for "variation of parameters".
 
  • #4
Why is this a second order differential equation? It is x' and not x''.
 
  • #5
Allright, my mistake, it should be

x'' + x = T, or something along those lines.

My question is: can I use Laplace transforms to solve endpoint value problems?
 
  • #6
HallsofIvy said:
I've always felt that "Laplace transform" was over rated. It gives a very "mechanical" way of solving problems that could be done in other ways. A problem like the one given here, to me, cries out for "variation of parameters".

I really like Laplace transforms. There's just something really cool and dare I say - transcendental - about how discontinuous areas on the t domain become continuous on the s domain. Although I'd suppose that's true of the integration transform too.

Also, it kind of blows my mind how similar T and sin(T) are on the s-domain.
 
  • #7
HallsofIvy said:
No, that is not an initial value problem. Since it is a second order differential equation, an "initial value problem" would have x and x' given at the same value of t. Since you are given x at two different values of t, that is a "boundary value problem" which is significantly harder than an initial value problem.

I've always felt that "Laplace transform" was over rated. It gives a very "mechanical" way of solving problems that could be done in other ways. A problem like the one given here, to me, cries out for "variation of parameters".
Agreed, the Laplace transform simply complicates matters more by introducing finding the inverse Laplace transform. There are much easier ways to solve ODE's and simpler ways of reducing PDE's.
 
  • #8
I think you can. Just leave x'(0) to be an unknown, then you should have a function back that is in terms of T and x'(0). Then apply the fact that x(4) = 7 to find the value of x'(0) which gives you the full equation back.

Laplace transforms, I think, solves exactly the same family of equations that the method of undetermined coefficients solves.
 

Related to Laplace Transforms to solve non IVPs?

1. What is a Laplace Transform?

A Laplace Transform is a mathematical operation that converts a function from the time domain to the frequency domain. It is particularly useful in solving differential equations, as it simplifies the problem by transforming the equation into a simpler algebraic equation.

2. How is a Laplace Transform used to solve non IVPs?

A Laplace Transform can be used to solve non IVPs (Initial Value Problems) by transforming the differential equation into an algebraic equation, which can then be solved using basic algebraic techniques. The resulting solution can then be transformed back to the time domain to obtain the solution to the original non IVP.

3. What types of non IVPs can be solved using Laplace Transforms?

Laplace Transforms can be used to solve a wide range of non IVPs, including ordinary differential equations (ODEs), partial differential equations (PDEs), and integral equations. They are particularly useful in solving linear differential equations with constant coefficients.

4. Are there any limitations to using Laplace Transforms to solve non IVPs?

While Laplace Transforms are a powerful tool for solving non IVPs, they do have some limitations. They are most effective for linear equations with constant coefficients, and may not work well for nonlinear or variable coefficient equations. Additionally, the initial conditions of the non IVP must be known in order to use a Laplace Transform to solve it.

5. Can Laplace Transforms be used to solve non IVPs with discontinuous functions?

Yes, Laplace Transforms can be used to solve non IVPs with discontinuous functions. However, the resulting solution may not be valid at the points of discontinuity. In these cases, it may be necessary to use other methods to find a solution that is valid at all points.

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