Transpose for vectorized implementation

[tkiefaber]

Hi all,

I completed the week 2 quiz but am still wondering how we determine when to transpose a matrix when going from a for loop implementation to a vectorized implementation.

For example:
a = np.random.randn(3,4)
b = np.random.randn(4,1)
c = a+b
and we create the for loop below
for i in range(3):
for j in range(4):
c[i][j]=a[i][j] + b[j]

I know that we transpose b when we create a vectorized implementation, but why is that? Does it have something to do with matrix multiplication or for loops that I’m missing?

Thanks a ton!

[TMosh]

Look at the sizes of the matrices.

Then transpose one of them if necessary in order that the ‘inner dimensions’ are the same.

That’s one of the rules of matrix algebra.

[TMosh]

For reference:

Matrix multiplication