某些增长速度函数

Question

in one of my note, instructor wrote the following function from increasing growth are sorted from left to right. but i couldn't understand it. i try to change it from image to text, but i failed. if someone help me, it's so nice. anyone could help me to give an equivalent formula for this notation?

again i'm sorry for using image.

Answer 1

My best assumption is that you don't know what the sigma, Σ means, so I'll help you with that.

It defines a series of expressions to add together.

So your look at your first first function, Σ 2/i

• First, you set i to be 1. You do this because of the i=1 below the Σ

• Second you add your function( 2/i ) to your result(which starts at 0)

• Increase i by 1 and repeat the second step. if i would be greater than n , then you stop

so if n is 4, your first sigma expression would be the following

2/1 + 2/2 + 2/3 + 2/4