Let us consider first an example of Morita equivalence; thus, for an integer , let be the algebra of
-matrices with entries in an algebra . The following is a typical example of Morita equivalence that involves noncommutative algebras.
Theorem 1.1Morita equivalence Lemma for arbitrary algebras
For any algebra and any integer , the algebras and are Morita equivalent.
Important Notes:
Even if is a commutative algebra, the algebra is of course not commutative for any because the matrix multiplication is generally non-commutative.
In general, the algebra cannot be recovered from its corresponding abelian category-mod. Therefore, in order for a concept in noncommutative geometry to have or retain an intrinsic meaning, such a concept must be Morita invariant that is, to remain within the same Morita equivalence class. This raises the important question: what properties of an algebra are Morita invariant ? The answer to this question is provided by the “Uniqueness Morita Theorem”.
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