Dot product of matrix with scalar

This is a trivial question.

I have a matrix

B = [1 1 1; 5 5 5; 9 9 9; 2 2 2; 6 6 6; 10 10 10; 3 3 3; 7 7 7; 11 11 11; 4 4 4; 8 8 8; 12 12 12];

n = [1,1,1]

How can I find the dot product of each row of B with n?

I know I can use for loops and do this for all rows of B:

 row1 = dot(B(i,:),n);

But there should be a better method using indexing......right? Using for loops isn't efficient.

Answer 1

[Titus Edelhofer]

Hi,

multiplying each row with a vector is nothing else but the matrix vector multiplication:

B*n'

(n' since your n is a row vector).

Titus

[Meghana Dinesh]

Right. works here.

What if I had another operation like minus?

I.e., if i want to subtract every row of B with n.

Resultrow_i = B(i,:)-n;

Or for any other algebraic operation for that matter...

[Stephen23]

It depends on the operation, but many binary operations (e.g. basic arithmetic and logical comparison) are supported by bsxfun:

>> B = [1 1 1; 5 5 5; 9 9 9; 2 2 2; 6 6 6; 10 10 10; 3 3 3; 7 7 7; 11 11 11; 4 4 4; 8 8 8; 12 12 12];
>> n = [1,1,1];
>> bsxfun(@minus,B,n)
ans =

      0    0    0
      4    4    4
      8    8    8
      1    1    1
      5    5    5
      9    9    9
      2    2    2
      6    6    6
     10   10   10
      3    3    3
      7    7    7
     11   11   11

[Meghana Dinesh]

Thanks!