A Simple Proof of the Fredholm Alternative and a Characterization of the Fredholm Operators

نویسنده

  • Alexander G. Ramm
چکیده

Let A be a linear bounded operator in a Hilbert space H, N(A) and R(A) its null-space and range, and A∗ its adjoint. The operator A is called Fredholm iff dim N(A) = dim N(A∗) := n < ∞ and R(A) and R(A∗) are closed subspaces of H. A simple and short proof is given of the following known result: A is Fredholm iff A = B + F , where B is an isomorphism and F is a finite-rank operator. The proof consists in reduction to a finite-dimensional linear algebraic system which is equivalent to the equation Au = f in the case of Fredholm operators.

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عنوان ژورنال:
  • The American Mathematical Monthly

دوره 108  شماره 

صفحات  -

تاریخ انتشار 2001