Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Double sum (Sigma) problem

  1. Sep 14, 2011 #1
    The problem statement, all variables and given/known data
    [itex]\sum_{k=1}^{3} \sum_{j=0}^{4}k^{j}[/itex]

    The attempt at a solution
    so this above means:
  2. jcsd
  3. Sep 14, 2011 #2
    It doesn't make a difference which order you do it in. You can see if you type the following in to matlab:

    syms k
    syms j




    the answer is 157 either way.
  4. Sep 14, 2011 #3
    so 1 more question
    [itex]\sum_{k=0}^{4} \sum_{j=1}^{5} (3^{k} + jk)[/itex]
    how to calculate this without Matlab.
    Should I transform it? (but have no idea how)
    or just have to put [0;4] for k, and [1;5] for j, and add everything ?
  5. Sep 14, 2011 #4
    You don't need to do a transform, if you start with the sum over j you will get

    \sum_{k=0}^{4} (3^k+1k+ ... 3^k+5k) = 0+ ...+ 3^4+20
  6. Sep 14, 2011 #5

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    It means the second one (which = 157); the first would be product_{k=1..3} sum_{j=0..4} k^j = 18755.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook