Calculating Indices: Solve the Mystery

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In summary, the picture shows how to calculate the product of two vectors. The first vector has indices that are the same as the second vector, so the product is summed over all the coordinates. When the indices are different, the product is only counted once.
  • #1
John Fennie
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Would anyone explain how the calculation in the picture was carried out? (the second equal sign)
I don't seem to be able to get the indices right.
 

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  • #2
John Fennie said:
Would anyone explain how the calculation in the picture was carried out? (the second equal sign)
I don't seem to be able to get the indices right.
When the indices are the same in both terms in a product, it means the product is summed/repeated over all the coordinates. When they are different, they are only counted once. Is that helpful?
 
  • #3
Is there any reason why the repeated indices are not placed in opposite directions (i.e. one „upstairs” and one „downstairs”)?
 
  • #4
dextercioby said:
Is there any reason why the repeated indices are not placed in opposite directions (i.e. one „upstairs” and one „downstairs”)?
Some authors (I know Schwartz does and mentions it in the preface of his QFT book) find it so obvious that repeated indices should be contracted using the metric that they resort to writing all indices in one position.
 
  • #5
I was suspecting an ##x_4 = ict ## there, so that is why I asked. I think Schwartz had a bad idea. There's elegance in using indices that way. Not to mention there is a difference between ## F_{\mu\nu}, F^{\mu\nu}, F_{\mu}^{~\nu}, F^{\nu}_{~\mu}##. How is that handled?
 
  • #6
It is quite clear that you can do whatever you want with free indices as long as you do it on both sides, so that is not a problem. When it comes to summation indices, it is clear that one needs to be taken as contravariant and the other as covariant and it really does not matter which is which so there is no possible misunderstanding there either. I am not saying I approve or that it is a good idea, just that there is no possible confusion if you know what you are doing.
 
  • #7
John Fennie said:
Would anyone explain how the calculation in the picture was carried out? (the second equal sign)
I don't seem to be able to get the indices right.
Hi yes, i understand that. But I am unable to work the math out, specifically the second +$\frac{1}{2}$
 
  • #8
Could you show your work please?
 

Related to Calculating Indices: Solve the Mystery

1. What is the purpose of calculating indices in "Solve the Mystery"?

The purpose of calculating indices in "Solve the Mystery" is to determine the unknown values in a given equation or problem. This helps to solve the mystery or puzzle presented in the activity.

2. How do you calculate indices?

Indices are calculated by using the laws of indices, also known as exponent rules. These rules include multiplying indices with the same base, dividing indices with the same base, and raising a power to a power. It is important to follow the correct order of operations when calculating indices.

3. What are some common mistakes when calculating indices?

Some common mistakes when calculating indices include forgetting to apply the rules of indices, using the wrong base or exponent, and mixing up the order of operations. It is important to double-check your work and make sure all rules are properly applied.

4. How can calculating indices be applied in real life?

Calculating indices is useful in many real-life situations, such as in finance and science. In finance, indices are used to track the performance of stocks and investments. In science, indices are used to represent large or small numbers, as well as in calculating rates of change and growth.

5. What are some tips for solving tricky index problems?

Some tips for solving tricky index problems include simplifying the expression as much as possible, breaking down the problem into smaller steps, and checking your work by plugging in values or using a calculator. It is also helpful to practice regularly and familiarize yourself with the laws of indices.

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