mxnet.np.dot

dot(a, b, out=None)

Dot product of two arrays. Specifically,

  • If both a and b are 1-D arrays, it is inner product of vectors

  • If both a and b are 2-D arrays, it is matrix multiplication,

  • If either a or b is 0-D (scalar), it is equivalent to multiply() and using np.multiply(a, b) or a * b is preferred.

  • If a is an N-D array and b is a 1-D array, it is a sum product over the last axis of a and b.

  • If a is an N-D array and b is a 2-D array, it is a sum product over the last axis of a and the second-to-last axis of b:

    dot(a, b)[i,j,k] = sum(a[i,j,:] * b[:,k])
Parameters

  • a (ndarray) – First argument.

  • b (ndarray) – Second argument.

  • out (ndarray, optional) – Output argument. It must have the same shape and type as the expected output.

Returns

output – Returns the dot product of a and b. If a and b are both scalars or both 1-D arrays then a scalar is returned; otherwise an array is returned. If out is given, then it is returned

Return type

ndarray

Examples

>>> a = np.array(3)
>>> b = np.array(4)
>>> np.dot(a, b)
array(12.)

For 2-D arrays it is the matrix product:

>>> a = np.array([[1, 0], [0, 1]])
>>> b = np.array([[4, 1], [2, 2]])
>>> np.dot(a, b)
array([[4., 1.],
       [2., 2.]])

>>> a = np.arange(3*4*5*6).reshape((3,4,5,6))
>>> b = np.arange(5*6)[::-1].reshape((6,5))
>>> np.dot(a, b)[2,3,2,2]
array(29884.)
>>> np.sum(a[2,3,2,:] * b[:,2])
array(29884.)