Can Infinitely Reordered Products Converge to Different Values?

In summary, the conversation discusses the convergence of the infinite product \prod^{\infty}_{n=1}(1-\frac{x^n}{n}) and its relationship to elliptic functions. It is noted that the product converges for |x|<1 and that the logarithm of the product can be expressed as an infinite sum of power series. The potential for reordering the series is mentioned, with caution for cases where the series only conditionally converges. It is also mentioned that Mathematica is unable to simplify the product except for trivial values of x.
  • #1
mmzaj
107
0
does the following infinite product converge ? and what to ?

[tex]\prod^{\infty}_{n=1}(1-\frac{x^n}{n})[/tex]

i know it has something to do with elliptic functions ...
 
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  • #2
I'm not sure except I believe so for |x|<1.
You can apply series test to the infinite sum you get by taking the logarithm of the infinite product.

Consider also the power series expansion:
[tex]\ln \left(1+z\right) = \sum_{k=1}^{\infty} (-)^{k+1}z^k[/tex]
for [itex] |z|<1[/itex].
So you can express the logarithm of your product as an infinite sum of power series.
See if reordering gives you an answer you can use.
 
  • #3
Be careful with reordering! If a series like that only conditionally converges, then by reordering, the series can converge to a different value (or even diverge).

If it helps, Mathematica is unable to simplify that product, except for trivial values of x.
 

FAQ: Can Infinitely Reordered Products Converge to Different Values?

What is an infinite product?

An infinite product is a mathematical expression that contains an infinite number of terms that are multiplied together. It can be written in the form of ∏n=1 an, where n represents the term number and an represents the term itself.

What does it mean for an infinite product to converge?

An infinite product converges if its value approaches a finite number as the number of terms approaches infinity. In other words, the product of an infinite number of terms becomes a finite number.

How can I determine if an infinite product converges or diverges?

To determine convergence or divergence of an infinite product, you can use various tests such as the Ratio Test, Root Test, and Comparison Test. These tests compare the given product to a known convergent or divergent series and provide a conclusive result.

Can an infinite product converge to a negative or complex number?

Yes, an infinite product can converge to a negative or complex number. The convergence of an infinite product depends on the values of the individual terms, not just their signs. So, it is possible for the product of negative or complex terms to result in a convergent value.

Are there any real-world applications of infinite product convergence?

Infinite product convergence has various applications in fields such as physics, engineering, and economics. For example, it is used in calculating probabilities in the field of statistics, in determining the stability of structures in engineering, and in estimating the value of stocks and investments in economics.

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