Does the permute function have a bug?

Question

Zhiyong Yang 2019-12-5

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/494939-does-the-permute-function-have-a-bug

评论： Steven Lord 2019-12-5

采纳的回答： David Goodmanson

Hi, when i use the permute function to shift dimensions of a four-dimension array, it has:

K>> U=randn(2,300,150,1000); U=permute(U,[4 1 2 3]); size(U)

ans =

1000 2 300 150

Why it doesnot shift the first dimension to forth dimension. Am i wrong or it is the issue of permute function. The matlab version is R2019b. Thanks!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

David Goodmanson 2019-12-5

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/494939-does-the-permute-function-have-a-bug#answer_404827

编辑：David Goodmanson 2019-12-5

Hello ZY,

see 'help permute'. Permute puts the dimensions in the order listed, so in this case the old 4th dimension goes first, old first dimension goes second, etc.

It could have been that each dimension goes to the dimension specified in its original slot, so that the first dimension goes fourth, the second dimension goes first. etc. That is a legit and consistent way of doing things, but it's not how it was done.

2 个评论
显示无隐藏无

Stephen23 2019-12-5

"Permute puts the dimensions in the order listed"

Just like indexing, which is interpreted in the same way: elements (or rows/columns/pages/...) are put into the order listed by the index. So permute is perfectly consistent with this.

Steven Lord 2019-12-5

在 MATLAB Online 中打开

Not only is that alternate interpretation a "legit and consistent way of doing things", it is the way that ipermute works. Showing this with a slightly smaller array:

>> U = ones(2, 3, 4, 5);
>> v = [4 1 2 3];
>> size(U)
ans =
     2     3     4     5
>> size(permute(U, v))
ans =
     5     2     3     4
>> size(ipermute(U, v))
ans =
     3     4     5     2