Find the orthogonal projection of a vector v onto U Let u be a unit vector in R^n and let U be the subspace spanned by u. Show that the orthogonal projection of a vector v onto U is given by proj_U v=(uu^T)v ,and thus that the matrix of this projection is uu^T. What is the rank of uu^T? Where u^T is the transpose of u. Any help is appreciate! I have no idea how to begin this other than knowing proj_(U)v = ((v, u)u)/((u, u))

Baardegem3Gw

Baardegem3Gw

Answered question

2022-12-01

Find the orthogonal projection of a vector v onto U
Let u be a unit vector in R n and let U be the subspace spanned by u. Show that the orthogonal projection of a vector v onto U is given by
proj U v = ( u u T ) v
and thus that the matrix of this projection is u u T . What is the rank of u u T ?
Where u T is the transpose of u. Any help is appreciate! I have no idea how to begin this other than knowing
proj U v = ( v , u ) u ( u , u )
Thanks!

Answer & Explanation

mirandalpz9Uw

mirandalpz9Uw

Beginner2022-12-02Added 10 answers

The projection formula you have is the solution. ( u , u ) = 1, since u is a unit vector. So
Proj U v = ( v , u ) u = ( u T v ) u = ( u u T ) v .
Lorena Becker

Lorena Becker

Beginner2022-12-03Added 1 answers

The general formula in any inner product space, whether u be a unit vector or not is
Proj U ( v ) = v , u u , u u = v , u u 2 u
Here u = 1, hence the formula comes down to
Proj U ( v ) = v , u u .
Now in R n equipped with the Euclidean inner product, v , u = t v u, when u and v are represented by column vectors.

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