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What does it mean when there is nothing on top of sigma?

User Satyadeep
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1 Answer

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The upper limit of summation is usually omitted when the index is obvious from the context.

Example: If we know
a_n is an infinite sequence (i.e. a function
a_n:\mathbb N\to\mathbb R, for instance), then we can denote the summation of all the terms in the sequence by


\displaystyle\sum_(n=1)^\infty a_n

or by


\displaystyle\sum_n a_n
User Cuong Ta
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