29.07.2014 Views

STATISTICS 512 TECHNIQUES OF MATHEMATICS FOR ...

STATISTICS 512 TECHNIQUES OF MATHEMATICS FOR ...

STATISTICS 512 TECHNIQUES OF MATHEMATICS FOR ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

26<br />

• Two vectors are orthogonal if the angle between<br />

them = ±2, equivalently if their scalar product<br />

=0. Wewritex ⊥ y.<br />

— Example: If z is any × 1 vector, and H is a<br />

hat matrix, then<br />

z = Hz +(I − H)z = z 1 + z 2 ,<br />

say, where z 1 ⊥ z 2 . The first is in col(X)<br />

(why?) and the second is in the space of vectors<br />

orthogonal to every vector in col(X). We<br />

write z 2 ∈ col(X) ⊥ . You should verify that<br />

this is a vector space (i.e. is closed under addition<br />

and scalar multiplication).<br />

• AmatrixQ × is orthogonal if the columns are<br />

mutually orthogonal, and have unit norm. Equivalently<br />

(why?)<br />

QQ 0 = Q 0 Q = I <br />

If Q is orthogonal then kQyk = kyk for any<br />

× 1vectory - “norms are preserved”. Similarly,<br />

angles between vectors are also preserved

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!