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

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SUMMARY

The dimension of the solution space for the heat equation, represented by the partial differential equation \(\frac{\partial U }{\partial t}=a^2\frac{\partial^2 U}{\partial x^2}\) with boundary conditions \(U(0,t) = U(L,t) = 0\) and initial condition \(U(x,0)= f(x)\), is infinite. This is due to the nature of solutions to partial linear homogeneous differential equations, which form an infinite-dimensional vector space because they involve unknown functions rather than constants. When boundary conditions are applied, the solution space becomes unidimensional, contingent upon \(f(x)=0\).

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

\frac{\partial U }{\partial t}=a^2\frac{\partial^2 U}{\partial x^2}

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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