(Trick Question: ) What is 0 · u ?
If the "0" is a scalar (which the non-bold type indicates) then this operation makes no sense.
If the "0" means the zero-vector (which means the zero should have been in bold face) then the result is the scalar 0.
The dot product is also defined for column matrices.
Let a = ( a1, a2 )T
Let b = ( b1, b2 )T
Then the dot product is defined as:
a · b = a1b1 + a2b2
Multiply corresponding elements of each column matrix, then add up the products. The result is a scalar value.
Sometimes the dot product of column matrices is written like this: aT b (but it is defined the same way). The reason for this second, odd notation will be apparent in a later chapter when matrix multiplication is discussed.
Here is an example: