[Numpy-discussion] dot product

Nils Wagner nwagner@iam.uni-stuttgart...
Tue Mar 10 04:37:49 CDT 2009

Hi all,

The dot product can be defined for two vectors x and y by
x·y=|x||y| \cos(\theta),

where theta is the angle between the vectors and |x| is
the norm.

Now assume that we have arrays(matrices)

X = [x_1, ..., x_m]

Y = [y_1, ..., y_s]

m <> s

Is there a built-in function to compute the following
matrix

for i in arange(0,m):
for j in arange(0,s):
MAC[i,j] =
dot(X[:,i],Y[:,j])**2/(dot(X[:,i],X[:,i])*dot(Y[:,j],Y[:,j]))

Each element of the matrix represents the corresponding
angle squared.

Nils