Colon-generated arrays with or without brackets

13 次查看（过去 30 天）
Alec Poulin
Alec Poulin 2018-3-27
编辑： Stephen23 2021-3-31
From what I can tell, the arrays a:d:b and [a:d:b] are exactly the same thing. For example,
>> [1:3] == 1:3
ans =
1×3 logical array
1 1 1
Yet, these two expressions give different results:
>> [1:3]' + 1:3
ans =
2 3
>> [1:3]' + [1:3]
ans =
2 3 4
3 4 5
4 5 6
Why?

请先登录，再回答此问题。

采纳的回答

Rik
Rik 2018-3-27
The reason for this is the unexpected order in which this statement is evaluated:
[1:3]' + 1:3
([1:3]' + 1):3
([1;2;3]+1):3
[2;3;4]:3
2:3
[2,3]
Adding the brackets forces the grouping before and after the colon operator (parentheses would have worked as well).
  9 个评论
显示 7更早的评论
Rik
Rik 2021-3-31
An error might break poorly coded functions that rely on this behavior. I think an mlint warning and warning when running the code would be better. If you use it as a shortcut, it will still work, but users will be warned about possibly unintended consequences. (similar to how if a<b<c triggers an mlint warning, but will run if you actually meant to use it like that (e.g. with a custom class that overloads lt))
Stephen23
Stephen23 2021-3-31
编辑：Stephen23 2021-3-31
@Rik: I suspect there is more code broken by this "feature" and time wasted debugging this rather unintuitive behavior, than gained by a few instances where it has been used intentionally (I do not recall ever seeing this).
MATLAB has tweaked other syntaxes over the years, this one is overdue for its retirement too.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Matrix Indexing 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by