Double Summation Result: \alpha^i\alpha^j

  • Thread starter feryee
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In summary, the result for the double summation ##\sum\limits_{i \neq j}^{\infty}\alpha^i\alpha^j## can be expressed as ##\frac{2\alpha}{(1+\alpha)(1-\alpha)^2}##. This can also be derived by expressing it as an iterated sum and applying the result for a sum of a geometric series. However, the person in the conversation was unable to get the same answer using this method and was asking for help.
  • #1
feryee
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what is the result for the following double summation:
##\sum\limits_{i \neq j}^{\infty}\alpha^i\alpha^j ##

where ## i, j =0,1,2,...##
 
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  • #2
Express it as an iterated sum and then apply the result for a sum of a geometric series. What do you get?
 
  • #3
micromass said:
Express it as an iterated sum and then apply the result for a sum of a geometric series. What do you get?
Well actually i have the final result but simply i couldn't get the same answer using geometric sum. Here is the final result:
##\frac{2\alpha}{(1+\alpha)(1-\alpha)^2}##

How is it possible.
 
  • #4
Have you tried anything? Where are you stuck?
 

1. What is a double summation?

A double summation is a mathematical operation where two summations are performed consecutively. This means that the sum of the first sequence is calculated, and then the sum of the resulting sequence is calculated.

2. What does the notation \alpha^i\alpha^j represent?

This notation represents the product of two variables, \alpha^i and \alpha^j, raised to the power of i and j respectively. In other words, it is equivalent to \alpha^{i+j}.

3. How is the result of a double summation calculated?

The result of a double summation is calculated by first evaluating the inner summation, which results in a single value. This value is then used as the variable in the outer summation, which ultimately produces the final result.

4. What are the uses of double summation in science?

Double summation is commonly used in various fields of science, such as mathematics, physics, and statistics. It is used to simplify and solve equations involving two variables, and it also has applications in discrete mathematics and calculus.

5. Are there any other types of summation besides double summation?

Yes, there are other types of summation, such as single summation, which involves only one sequence, and multiple summation, which involves more than two sequences. There are also various methods and formulas for calculating summations, depending on the specific scenario and application.

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