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  2. Mathematical notation for a conditional sum

    math.stackexchange.com/questions/99344

    Although I don't think it is quite mainstream, but you could look into Iverson Notation. In short, you have a bracket and inside you write a condition. The bracket value is 1 if the condition holds, otherwise it's 0. Its most popular usage was in Concrete Mathematics (by Knuth et al). n(A) = ∑F∈A wF[AF ≠ NULL] ∑F∈AwF n (A) = ∑ F ∈ ...

  3. You will often see the terms in a general sum referred to as "addends" or "summands". Your suggestion regarding subtraction/division as compared to addition/mulipilication is as good as any. The roles of the operands are not interchangeable, so a single description isn't really appropriate.

  4. Mathematics Stack Exchange

    math.stackexchange.com

    1. modified 1 hour ago. 1 vote. 1 answer. 19 views. To prove if there exists a linear transformation that takes a high dimensional complex vector to a scalar injectively. complex-analysis. Matsmir. 3,570.

  5. summation - Rules of Double Sums - Mathematics Stack Exchange

    math.stackexchange.com/questions/2416833/rules-of-double-sums

    Hence. 2PURPLE + BLACK = (m ∑ i = 1xi)2. where. PURPLE = ∑ i <jxixj and BLACK = m ∑ i = 1x2i. 1 and 2 imply. ∑ i <jxixj = 1 2[(m ∑ i = 1xi)2 − (m ∑ i = 1x2i)]. This shows up whenever you want to evaluate a sum in two indices where one index is the other. This shows up for instance in probability and combintorics. Share.

  6. I would use a matrix-notation. I assume your original values are in a vector S, say $ S=[a,b,c,d] $ and then I'd express the transformation to the vector Q using the triangular matrix D with

  7. Sum of a power series $n x^n$ - Mathematics Stack Exchange

    math.stackexchange.com/questions/647587

    Multiply both sides with x x and you will get. ∑n=0∞ nxn = x (1 − x)2 ∑ n = 0 ∞ n x n = x (1 − x) 2. But as the first summand for n = 0 n = 0 is zero this is the same as. ∑n=1∞ nxn = x (1 − x)2 ∑ n = 1 ∞ n x n = x (1 − x) 2. For |x| ≥ 1 | x | ≥ 1 the limit of nxn n x n does not tend to zero, thus the series ∑∞ n ...

  8. The idea behind the sum of powers of 2 - Mathematics Stack...

    math.stackexchange.com/questions/1990137

    I know that the sum of powers of $2$ is $2^{n+1}-1$, and I know the mathematical induction proof. But does anyone know how $2^{n+1}-1$ comes up in the first place. For example, sum of n numbers is $\frac{n(n+1)}{2}$. The idea is that we replicate the set and put it in a rectangle, hence we can do the trick.

  9. linear algebra - Difference between sum and direct sum -...

    math.stackexchange.com/questions/1163318/difference-between-sum-and-direct-sum

    Direct sum is a term for subspaces, while sum is defined for vectors. We can take the sum of subspaces, but then their intersection need not be {0} {0}. Example: Let u = (0, 1), v = (1, 0), w = (1, 0) u = (0, 1), v = (1, 0), w = (1, 0). Then. u ⊕ v u ⊕ v makes no sense in this context. Note that the direct sum of subspaces of a vector space ...

  10. Can we express sum of products as product of sums?

    math.stackexchange.com/questions/1433059

    41. In general, one can write a product of sums as a sum of a products: (∑ i ∈ Ixi)(∑ j ∈ Jyj) = ∑ i ∈ I, j ∈ Jxiyj. One cannot, however, in general reverse this process, that is, write a sum of products, (∗) ∑ k ∈ Kxkyk, (∗) as a product of sums. (In this answer we assume that the index sets, I, J, etc., are finite ...

  11. How to understand sum symbol? - Mathematics Stack Exchange

    math.stackexchange.com/questions/477421

    $\sum_{i=m}^n a_i = a_m + a_{m+1} + a_{m+2} +\cdots+ a_{n-1} + a_n.$ Where, i represents the index of summation; a_i is an indexed variable representing each successive term in the series; m is the lower bound of summation, and n is the upper bound of summation. The "i = m" under the summation symbol means that the index i starts out equal to m.