How to multiply two rows or columns?

Question

a = [1, 2, 3];
b = [3, 2, 1];
c = a * b;

yields

error: operator *: nonconformant arguments (op1 is 1x3, op2 is 1x3)

Why can I not multiply these two rows of the same size? I shouldn't have to run a for loop for this, but I don't know of another way...

I saw section 1.2.3 here, which indicates (to me at least) that I should be able to do it.

Answer 1

You made 2 rows, which can't be multiplied together.

The general form of matrix multiplication is "Row-Dot-Column", which means take the dot product of each row with each column. In your case you have 1 row, but 3 columns (which doesn't work!).

a = [1, 2, 3];
b = [3, 2, 1];
c = a' * b;

ans =

 3     2     1
 6     4     2
 9     6     3

Answer 2

I see now that there is a .* operator. I did not know where to find that in the documentation, and it does what I want.