square of a vector

I have to calculate a square of vector which should results a scalar value. i.e) A=(B-C)^2 B and C are vectors and I need A as a scalar. How can I implement this in matlab??

Answer 1

[Honglei Chen]

My guess is you need an inner product, i.e. A = |B-C|^2, you can do it many different ways, one way is

B = ones(3,1);
C = ones(3,1);
A = (B-C)'*(B-C)

[Berbia]

I got it...Can I use dot(B,C)? Is both are same?

[Honglei Chen]

yes they are the same, but you should use

dot(B-C,B-C)

[Matt J]

No. You could do dot(B-C,B-C) or, more efficiently

tmp=B-C;
A=dot(tmp,tmp);

The DOT command is relatively slow, though, in case that matters.

[Berbia]

Thanks a lot...I have to do this operation repeatedly in loop. which is more efficient, whether tmp=B-C; dot(tmp,tmp); or norm(B-C)^2?

[Honglei Chen]

I'd say

temp = B-C;
temp'*temp

[Matt J]

You should think about whether the loop can be avoided altogether, since this sounds like a very vectorizable operation. If B and C are matrices and you want the dot product along columns, for example

temp=B-C;
result = sum(temp.^2,1);

Answer 2

[Matt J]

 A=norm(B-C)^2;