[英]Numpy dot one matrix with an array of vectors and get a new array of vectors
Say we have an array of 2D vectors (describing a square shape), and a matrix (scale along y axis):假设我们有一个二维向量数组(描述一个正方形)和一个矩阵(沿 y 轴缩放):
vecs = np.array([[1, 0],
[1, 1],
[0, 1],
[0, 0]])
mat = np.array([[1, 0],
[0, 2]])
I want to get a new array of vectors, where each vector from vecs
is dot multiplied with mat
.我想得到一个新的向量数组,其中来自
vecs
的每个向量都与mat
相乘。 Now I do it like this:现在我这样做:
new_vecs = vecs.copy()
for i, vec in enumerate(vecs):
new_vecs[i] = np.dot(mat, vec)
This produces the desired result:这会产生所需的结果:
>>> print(new_vecs)
[[1 0]
[1 2]
[0 2]
[0 0]]
What are better ways to do this?有什么更好的方法来做到这一点?
The dot product np.dot
will multiply matrices of any shape with each other, as long as their shapes line up: np.dot((a,b), (b,c)) -> (a,c)
. 点积
np.dot
将将任意形状的矩阵彼此相乘,只要它们的形状np.dot((a,b), (b,c)) -> (a,c)
: np.dot((a,b), (b,c)) -> (a,c)
。 So if you invert the order, Numpy does this for you in one call: 因此,如果您颠倒订单,Numpy会在一个电话中为您完成此操作:
In [3]: np.dot(vecs, mat)
Out[3]:
array([[1, 0],
[1, 2],
[0, 2],
[0, 0]])
You can use the following:您可以使用以下内容:
np.dot(mat , vecs.T).T
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