使numpy的特殊的对角矩阵 [英] Make special diagonal matrix in Numpy

问题描述

我试图做一个numpy的数组，它看起来像这样：

I am trying to make a numpy array that looks like this:

[a b c       ]
[  a b c     ]
[    a b c   ]
[      a b c ] 

因此​​，这涉及到更新主对角线和两条对角线上方

So this involves updating the main diagonal and the two diagonals above it.

什么是这样做的有效途径？

What would be an efficient way of doing this?

推荐答案

您可以使用 np.indices 来得到你的数组的索引，然后分配值，你在哪里想要的。

You can use np.indices to get the indices of your array and then assign the values where you want.

a = np.zeros((5,10))
i,j = np.indices(a.shape)

I，J 是行和列的索引，分别为。

i,j are the line and column indices, respectively.

a[i==j] = 1.
a[i==j-1] = 2.
a[i==j-2] = 3.

将导致：

array([[ 1.,  2.,  3.,  0.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  1.,  2.,  3.,  0.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  1.,  2.,  3.,  0.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  1.,  2.,  3.,  0.,  0.,  0.,  0.],
       [ 0.,  0.,  0.,  0.,  1.,  2.,  3.,  0.,  0.,  0.]])

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