Hi!
Can someone please explain what the subscript 2 in the notation of 
means?
I get that the superscript 2 stands for squaring, but I don’t get what the subscript 2 means.
It shows the type of “norm”. which is the way to calculate the distance.
“2” represents L2 norm, as known as the Euclidean distance, and the square root of the sum of the squared values. “1” represent L1 norm, as known as the Manhattan distance, and the sum of the absolute values.