numpy.dot¶
-
numpy.
dot
(a, b, out=None)¶ Dot product of two arrays.
对于2-D数组,其等效于矩阵乘法,对于1-D数组等效于向量的内积(无共轭复数)。对于N维,它是a的最后一个轴和b的倒数第二个轴的积的和:
dot(a, b)[i,j,k,m] = sum(a[i,j,:] * b[k,:,m])
Parameters: a : array_like
First argument.
b : array_like
Second argument.
out : ndarray, optional
Output argument. 如果没有使用,返回必须有确切的类型。特别地,它必须具有正确的类型,必须是C连续的,并且其dtype必须是dot(a,b)将返回的dtype。This is a performance feature. Therefore, if these conditions are not met, an exception is raised, instead of attempting to be flexible.
Returns: output : ndarray
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.
引发: ValueError
如果a的最后一个维度大小与b的倒数第二个维度的大小不同。
另见
Examples
>>> np.dot(3, 4) 12
Neither argument is complex-conjugated:
>>> np.dot([2j, 3j], [2j, 3j]) (-13+0j)
For 2-D arrays it is the matrix product:
>>> a = [[1, 0], [0, 1]] >>> b = [[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(3*4*5*6)[::-1].reshape((5,4,6,3)) >>> np.dot(a, b)[2,3,2,1,2,2] 499128 >>> sum(a[2,3,2,:] * b[1,2,:,2]) 499128