Tutorial Video
Element by Element Multiplication
Element by element multiplication (the dot product) .*
works differently from Array multiplication *
be careful not to confuse the two.
Multiplication of Scalars
Assuming one buys 5 pens and the price of a pen is £2. Then the amount of cash spent on pens is £10
5 pens .* £2 = 5*£2 = £10
To write this in MATLAB we would use
5.*2
Note for a 1 by 1 scalar array multiplication and element by element multiplication are identical.
(Dot Product) of Column Vectors
If we ordered 5 pens which cost £2 each and 3 pads which cost £6 each then
i.e. we would spend a total of £10 on pens and £18 on pads.
To write this in MATLAB we would use
[5;3].*[2;6]
(Dot Product) of Matrices
If the man in the red house bought 5 pens and 3 pads and the women in the green house bought 7 pens and 5 pads from the same shop costing £2 a pen and £6 a pad then:
i.e. the man spent £10 on pens and £18 on pads and the woman spent £14 on pens and £30 on pads.
To write this in MATLAB we would use
[5,7;3,5].*[2,2;6,6]
Alternatively if the woman living in the green house went to a more expensive shop where the price of pens and pads was £3 and £7 respectively
i.e. the man would once again spend £10 on pens and £18 on pads and this time the woman would spend £21 on pens and £35 on pads.
To write this in MATLAB we would use
[5,7;3,5].*[2,3;6,7]