# Math Help - Hermitian Matrix

1. ## Hermitian Matrix

Let M be an nxn complex orthogonal matrix. Show that for any two column vectors v, w in C,

show that v * w = (Mv) * (Mw)

where * denotes the dot product.

I'm stuck. I know that any vector v^H = v^-1

Thanks

2. ## Re: Hermitian Matrix

one way to write x*y in matrix form is:

xHy (where xH is thus a row vector, instead of a column vector, and consists of the complex conjugates of coordinates of x)

thus (Mu)*(Mv) = (Mu)H(Mv) = uHMHMv.

if M is a complex orthogonal (unitary) matrix, then MHM = I,

whence (Mu)*(Mv) = uHv = u*v.

(your equation vH = v-1 makes no sense, vectors do not usually HAVE inverses, since vector multiplication is not generally defined).