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Equidimensional ODE

A linear 2nd order ODE is equidimensional when it has the form where are constants.

Definition 6.16 (Linear 2nd Order Equidimensional ODE)

A linear 2nd order ODE is equidimensional if it is of the form

where are constants.

Scaling property and solving

The scaling property: if is a solution of the homogeneous equidimensional ODE with , then so is for any constant .

Proof. By the chain rule, and , so

with , since solves the homogeneous equation.

Solving. Since , the function is an eigenfunction of with eigenvalue . Trying in the homogeneous equation gives

For distinct roots the complementary functions are

Equivalently, substituting turns the ODE into one with constant coefficients,

whose characteristic equation is the same as above. For the degenerate case ,

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