My Math Forum  

Go Back   My Math Forum > High School Math Forum > Elementary Math

Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion

Thanks Tree1Thanks
  • 1 Post By JeffM1
LinkBack Thread Tools Display Modes
August 28th, 2017, 09:10 PM   #1
Joined: Jul 2017
From: europe

Posts: 51
Thanks: 0

Double sigma

I am reading my Bulgarian textbook about Electromagnetism theory. I found an expression, which I can't understand. Here I attached the expression to my post.
Please, help me to understand this "double" sum from pure mathematical point of view. What does the expression mean?
I will be very thankful for a step-by-step explanation of this particular case of double sum.

Wish you a nice day everybody!
Attached Images
File Type: gif CodeCogsEqn (8).gif (1.0 KB, 26 views)
DesertFox is offline  
August 29th, 2017, 01:13 PM   #2
Global Moderator
Joined: May 2007

Posts: 6,511
Thanks: 585

Your expression has 2 indices p and q. The double sum is simply summing over both of them. It is a standard notation, nothing to do with Bulgarian.
mathman is offline  
August 29th, 2017, 01:56 PM   #3
Senior Member
Joined: May 2016
From: USA

Posts: 1,030
Thanks: 420

$\displaystyle \sum_{i=1}^3 \sum_{j=1}^3 i(2j+1) = \sum_{i=1}^3(3i + 5i +7i) = 15 * \sum_{i=1}^3i = 15(1 + 2 + 3) = 90.$
Thanks from Country Boy
JeffM1 is offline  
September 3rd, 2017, 12:06 PM   #4
Math Team
Joined: Jan 2015
From: Alabama

Posts: 3,170
Thanks: 869

Since addition and multiplication "distribute" and addition is commutative, the order is not relevant. You can also do it as
$\displaystyle \sum_{j= 1}^3 (2j+ 1)\left(\sum_{i= 1}^3 i\right)=$$\displaystyle \sum_{j=1}^3 (2j+ 1)(1+ 2+ 3)=$$\displaystyle \sum_{j=1}^3 6(2j+ 1)= 6(3)+ 6(5)+ 6(7)= 18+ 30+ 42= 90$.

$\displaystyle \sum_{p= 1}^{m_p}\sum{q= 1}^{m_q} M_{pq} \frac{di_q}{dt}= \sum_{p=1}^{m_p}\left(M_{p1}\frac{di_1}{dt}+ M_{p2}\frac{di_2}{dt}+ \cdot\cdot\cdot+ M_{pm_q} M_{pm_q}\frac{di_{mq}}{dt}\right)= \left(M_{11}\frac{di_1}{dt}+ M_{21}\frac{di_1}{dt}+ \cdot\cdot\cdot+ M_{m_p1}\frac{di_1}{dt}\right)+ \left(M_{12}\frac{di_2}{dt}+ M_{22}\frac{di_2}{dt}+ \cdot\cdot\cdot+ M_{m_p2}\frac{di_2}{dt}\right)+ \cdot\cdot\cdot+ \left(M_{1m_q}\frac{di_{m_q}}{dt}+ M_{2m_q}\frac{di_{m_q}}{dt}+ \cdot\cdot\cdot+ M_{m_pm_q}\frac{di_{m_q}}{dt}\right)$
Country Boy is offline  

  My Math Forum > High School Math Forum > Elementary Math

double, sigma

Thread Tools
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
Sigma Demigodvampire098 Probability and Statistics 2 September 1st, 2015 01:07 PM
Double sigma question ishita1607 Algebra 3 October 6th, 2013 04:53 AM
how to find : sigma f/sigma x luketapis Calculus 2 March 27th, 2012 11:30 AM
Six Sigma rudrax Economics 1 May 26th, 2011 01:09 AM

Copyright © 2018 My Math Forum. All rights reserved.