Projection

• Let be a vector space and . A function is called a projection on if

  • There exists such that . [^oplus]
  • For where and we have

• (Friedberg e2.1.22) is linear

• (Frieidberg e2.1.23) If , then so that

• (Friedberg e2.3.14) is a projection if and only if (that is, applying the projection twice has the same effect as applying it once)

• A linear operator on is called nilpotent if for some positive integer .

Links §

• Friedberg, Insel and Spence