Dimension of Soln Space of Heat Equation: Is It Infinite?

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Discussion Overview

The discussion revolves around the dimensionality of the solution space for the heat equation, specifically under given boundary conditions. Participants explore whether this space is infinite-dimensional or not, considering both the nature of the differential equation and the implications of boundary conditions.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant questions whether the dimension of the solution space for the heat equation is infinite, seeking clarification on the reasoning behind it.
  • Another participant asserts that solutions to an nth order linear homogeneous differential equation form an n-dimensional vector space, while solutions to partial linear homogeneous differential equations are infinite-dimensional due to the presence of unknown functions instead of constants.
  • A different viewpoint suggests that the solution to the heat equation is unique, implying that the solution space is one-dimensional and consists of a single vector.
  • Additionally, a participant notes that without boundary conditions, the solution space is infinite-dimensional, but with the specified boundary conditions, it becomes non-dimensional and not a vector space unless the initial condition f(x) equals zero.

Areas of Agreement / Disagreement

Participants express differing opinions on the dimensionality of the solution space, with some arguing for infinite dimensionality and others claiming it is one-dimensional or non-dimensional under certain conditions. No consensus is reached.

Contextual Notes

The discussion highlights the dependence on boundary conditions and initial conditions, as well as the distinction between ordinary and partial differential equations, which may affect the dimensionality of the solution space.

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What is the dimension of soln space of the heat equation:

[tex]\frac{\partial U }{\partial t}=a^2\frac{\partial^2 U}{\partial x^2}[/tex]

U(0,t) = U(L,t) = 0
U(x,0)= f(x)

Is it infinite , if so why?
 
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The set of all solutions to an nth order linear homogeneous differential equation forms an n dimensional vector space because the solutions can be written with n constants.

The set of all solutions to any partial linear homogenous differential equation form an infinite dimensional vector space because instead of unknown constants, you have unknown functions.
 
The solution to that PDE is unique.So the solution space is unidimensional and moreover formed from only one vector.

Daniel.
 
To compliment the post above, without the boundary conditions the space is infinite dimensional and with the boundary conditions it is nondimensional i.e. not a vector space unless f(x)=0.
 

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