Primary Decomposition

Definition

Primary decomposition refers to the process of expressing an ideal in a ring as an intersection of primary ideals, where each primary ideal corresponds to a unique prime ideal. This concept is crucial in understanding how irreducible varieties can be analyzed through their component parts, allowing for a deeper exploration of algebraic structures and their properties.

5 Must Know Facts For Your Next Test

1. The primary decomposition theorem states that any ideal can be expressed as an intersection of primary ideals associated with distinct prime ideals.
2. In primary decomposition, each primary ideal contributes to the structure of the original ideal, allowing for better understanding and manipulation of algebraic varieties.
3. The primary components are unique up to radical ideals, meaning they can vary but maintain their essential properties.
4. The concept connects deeply with algebraic geometry, particularly when analyzing the irreducibility of varieties and their singularities.
5. In commutative algebra, primary decomposition plays a significant role in computing the dimension and depth of modules over a ring.

Review Questions

• How does primary decomposition help in analyzing the structure of algebraic varieties?
  • Primary decomposition allows us to break down an ideal into primary components, making it easier to study its properties. Each primary ideal corresponds to a specific prime ideal, enabling a clearer understanding of the underlying geometric structure. By analyzing these components, we can gain insights into the irreducibility and singularities of varieties.
• Discuss the relationship between primary ideals and prime ideals in the context of primary decomposition.
  • In primary decomposition, each ideal can be expressed as an intersection of primary ideals, which are tied to prime ideals. A primary ideal's structure reflects its associated prime ideal, where the primary ideal captures more nuanced information about the geometric or algebraic properties of the variety. This relationship helps mathematicians classify and study algebraic structures effectively.
• Evaluate the significance of primary decomposition in understanding depth and regular sequences within Cohen-Macaulay rings.
  • Primary decomposition plays a crucial role in Cohen-Macaulay rings by allowing us to analyze the depth and regular sequences more effectively. The ability to decompose ideals into primary components helps establish criteria for regularity and provides insights into projective dimensions. This understanding deepens our grasp of how these rings behave under various algebraic operations and their implications for algebraic geometry.

Related terms

Primary Ideal: An ideal I in a ring R is primary if whenever the product ab is in I, then either a is in I or b^n is in I for some n > 0.

Prime Ideal: An ideal P in a ring R is prime if whenever the product ab is in P, then at least one of a or b is in P. It serves as a key building block for the structure of the ring.

Radical Ideal: An ideal I in a ring R is radical if whenever x^n is in I for some n > 0, then x is also in I. It relates closely to the concept of primary decomposition.