What Is the Closure of Modules Theorem in Several Complex Variables?

In summary, the "closure of modules" theorem in several complex variables states that a germ of a function belongs to the stalk of an ideal at a point if it can be uniformly approximated on neighborhoods of that point by functions whose stalks lie in the ideal. The hypothesis can be strengthened by assuming that there is a compact neighborhood where the function can be approximated arbitrarily well in the sup norm by functions with germs in the ideal. This theorem also involves finding a sequence of coefficient functions and a normal family argument to establish a bound on the limiting coefficients. Unfortunately, there is limited information about this topic available on the web.
  • #1
mathwonk
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can anyone give me a precise statement of the "closure of modules" theorem in several complex variables? it says something like: a criterion for the germ of a function to belong to the stalk of an ideal at a point, is that the function can be uniformly approximated on neighborhoods of that point by functions whose stalks do lie in the ideal. I have forgotten my gunning and rossi.
so it is something like, if for every e>0 there is a nbhd V of p and a function in the ideal I which is uniformly closer to f than e on V, then f belongs to I.

? And are there some bounds on the coefficients of the generators of the ideal in terms of given bounds on the coefficients of the approximating functions?
 
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  • #2
well i will answer my own question. the hypothesis i gave seems too weak. rather one apparently needs to assume that there is some compact nbhd of p on which f can be approximated arbitrarily well in the sup norm by functions with germs in the ideal.

then one finds a nbhd where there are functions defined whose germs generate the ideal, and then one takes a sequence of approximations, which means a sequence of coefficient functions in terms of these fixed generators, and then one finds a convergent subsequence of coefficient functions on some smaller nbhd using a normal family argument.

then the bound on the limiting coefficients comes from the bounds on the function and its approximations.

apparently this stuff on several complex variables is not so well represented on the web, wikipedia and so on... a pity. although there was a book by joe taylor for sale on amazon with a selective excerpt visible.
 

Related to What Is the Closure of Modules Theorem in Several Complex Variables?

1. What is the Closure of Modules Theorem?

The Closure of Modules Theorem is a mathematical property that states that the closure of a set of modules under a certain operation is also a module.

2. What is the importance of the Closure of Modules Theorem?

The Closure of Modules Theorem is important because it allows us to determine whether a set of modules is closed under a given operation, which is essential in understanding the behavior of modules in algebraic structures.

3. How is the Closure of Modules Theorem used in real life?

The Closure of Modules Theorem has many applications in fields such as physics, engineering, and computer science. It is used to analyze the behavior of systems that can be represented by modules, such as electrical circuits and software programs.

4. Can the Closure of Modules Theorem be applied to other mathematical structures?

Yes, the Closure of Modules Theorem can be extended to other algebraic structures such as rings, fields, and vector spaces. However, the specific conditions and properties may differ depending on the structure.

5. Are there any limitations or exceptions to the Closure of Modules Theorem?

Yes, the Closure of Modules Theorem may not hold for certain types of modules or operations. For example, it may not hold for infinite modules or non-commutative operations. It is important to carefully consider the specific conditions and properties in each application of the theorem.

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