Deep Neural Net simple explanation (NN 1)

Nueral net understanding.Draw a line that seperates blue and red shackles

matrix transpose example (DL)

Transpose

Getting the transpose of a matrix is really easy in NumPy. Simply access its T attribute. There is also a transpose() function which returns the same thing, but you’ll rarely see that used anywhere because typing T is so much easier. :)

For example:

m = np.array([[1,2,3,4], [5,6,7,8], [9,10,11,12]])
m
# displays the following result:
# array([[ 1,  2,  3,  4],
#        [ 5,  6,  7,  8],
#        [ 9, 10, 11, 12]])

m.T
# displays the following result:
# array([[ 1,  5,  9],
#        [ 2,  6, 10],
#        [ 3,  7, 11],
#        [ 4,  8, 12]])

NumPy does this without actually moving any data in memory - it simply changes the way it indexes the original matrix - so it’s quite efficient.

However, that also means you need to be careful with how you modify objects, because they are sharing the same data. For example, with the same matrix m from above, let's make a new variable m_t that stores m's transpose. Then look what happens if we modify a value in m_t:

m_t = m.T
m_t[3][1] = 200
m_t
# displays the following result:
# array([[ 1,   5, 9],
#        [ 2,   6, 10],
#        [ 3,   7, 11],
#        [ 4, 200, 12]])

m
# displays the following result:
# array([[ 1,  2,  3,   4],
#        [ 5,  6,  7, 200],
#        [ 9, 10, 11,  12]])

Notice how it modified both the transpose and the original matrix, too! That's because they are sharing the same copy of data. So remember to consider the transpose just as a different view of your matrix, rather than a different matrix entirely.