change of basis coordinates

Hi all,

I have an orthogonal basis consisting of the following vectors in C^4 -

[0,1,0,-1] , [1,0,0,0] , [0,0,i,0]

Now, I have the vector [1, -i, 0, i] in standard coordinates. I wish to express this vector with respect to my orthogonal basis.

So, I solve c1 [0,1,0,-1] + c2 [1,0,0,0] + c3 [0,0,0,0] + c4[0,0,i,0] = [1, -i, 0, i].

[c1,c2,c3,c4] will be the vector wrt my othogonal basis.

Is this correct?

Thanks.

Re: change of basis coordinates

Hey sfspitfire23.

Have you set up your augmented system? (Hint: Setup the augmented system [A | b] and solve for [I | x])

Re: change of basis coordinates

IF (1,-i,0,i) is in the span of your three vectors, then you only need to solve:

c_{1}(0,1,0,-1) + c_{2}(1,0,0,0) + c_{3}(0,0,i,0) = (1,-i,0,i) for c_{1},c_{2} and c_{3} (adding a 0-vector to a basis is a waste of time).

inspection of the first coordinate shows c_{2} = 1. inspection of the fourth coordinate shows c_{1} = -i.

finally, since (-i)(0,1,0,-1) + (1)(1,0,0,0) = (0,-i,0,i) + (1,0,0,0) = (1,-i,0,i), we conclude c_{3} = 0, so our coordinates in this basis are [-i,1,0].

note you only specified THREE basis vectors, so we only have THREE coordinates (that is, if our basis only has 3 elements, the span of this basis is a 3-dimensional subspace of C^{4}).

Re: change of basis coordinates

Deveno,

Thanks. Is including the zero vector technically wrong? Or is it just redundant?

Re: change of basis coordinates

including a 0 vector makes a set linearly dependent.