TITLE: What does the math notation $\sum$ mean?
QUESTION [11 upvotes]: I have come across this symbol a few times, and I am not sure what it "does" or what it means:
$\Large\sum$

REPLY [2 votes]: Coming from a programming background, I found it quite helpful to explain it using a for loop:
The mathematician would write it like this:
$\sum\limits_{i=m}^n f(i)$
And the programmer would write it like this:
result = 0
for (i=m; i<=n; i++) {
    result += f(i)
}

You can think of m as the start index and n as the end index.