1

In 'Elements of Statistical Learning' Chapter 14 (p. 503), objects $i$ and $i'$ and further $x_i$, $x_i'$ are commonly referred to. However I don't think they are explicitly defined. What could be the meaning of this symbol: $'$

I think it could possibly be that $x_i$ and $x_i'$ are different objects in the same set but am not sure.

Source: Friedman, J., Hastie, T., & Tibshirani, R. (2001). The elements of statistical learning (Vol. 1, No. 10). New York: Springer series in statistics.

Thelonious Monk
  • 123
  • They are only two different objects: $x$ and $x'$ and also $x_i$ and $x_i '$ – Mauro ALLEGRANZA Jun 04 '20 at 10:31
  • Be careful here: the objects are indexed by $i$ or $i^\prime$, while $x_i$ is the family of attribute values of the object $i$. Hence it may well happen that $x_i=x_k$ for $i\neq k$. – Hagen Knaf Jun 04 '20 at 11:02
  • Usually $i^2=-1$, but $i'$ may be something different. For indices, some people write $x_i,x_i'$ for $x_i,x_j$. As a function in $t$, $x_i'(t)$ is the derivative. For matrices, $X'$ is often the transpose of $X$. So there are several meanings of the symbol $'$. – Dietrich Burde Jun 04 '20 at 11:06

0 Answers0