What is the Dimension of a Symmetric Tensor Vector Space?

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SUMMARY

The dimension of a symmetric tensor vector space \( V_n \) with indices ranging from 1 to 3 is determined by analyzing the combinations of indices in the tensor \( S^{a_1 \ldots a_n} \). Specifically, the problem involves partitioning \( n \) indices into groups of 1's, 2's, and 3's, represented as \( S^{\underbrace{1...1}_{s} \underbrace{2...2}_{r} \underbrace{3...3}_{t}} \) where \( r+s+t=n \). The solution requires understanding the combinatorial arrangements of these indices to find the number of independent components of the tensor.

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Homework Statement



Having a symmetric tensor S^{a_1 ...a_n} forming a vector space V_n with indices taking values from 1 to 3; what is the dimension of such a vector space?

Homework Equations


The Attempt at a Solution



essentially this reduces to picking a tensor of type S^{ \underbrace{1...1}_{s} \underbrace{2...2}_{r} \underbrace{3...3}_{t}} with r+s+t =n and seeing how many non isomorphic combinations there are. I'm not that skilled at combinatorics unfortunately
 
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So... if I'm understanding correctly, this is a slightly roundabout way to ask how many independent components the tensor S has?

Think about it this way: you have a list of n indices which you need to split into a set of 1's, a set of 2's and a set of 3's, in that order. How many places can you choose to put the split between the 1's and the 2's?

Then, given that choice, how many places can you choose to put the split between the 2's and the 3's?
 
worked it out a different way, thanks all the same
 

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