all function B = all(A < 0.5,3)

3 次查看（过去 30 天）
Marie Nancy B
Marie Nancy B 2023-6-14
编辑： Stephen23 2023-6-15
Ran in:
This is straight forward to me:
A = [0.53 0.67 0.01 0.38 0.07 0.42 0.69]
A = 1×7
0.5300 0.6700 0.0100 0.3800 0.0700 0.4200 0.6900
B = all(A < 0.5,1)
B = 1×7 logical array
0 0 1 1 1 1 0
this also makes sense -
A = [0.53 0.67 0.01; 0.38 0.07 0.42 ]
A = 2×3
0.5300 0.6700 0.0100 0.3800 0.0700 0.4200
B = all(A < 0.5,2)
B = 2×1 logical array
0 1
But why does this yield the same result?
A = [0.53 0.67 0.01 1.1; 0.38 0.07 0.42 0.01]
A = 2×4
0.5300 0.6700 0.0100 1.1000 0.3800 0.0700 0.4200 0.0100
B = all(A < 0.5,3)
B = 2×4 logical array
0 0 1 0 1 1 1 1
OR
B = all(A < 0.5,4)
B = 2×4 logical array
0 0 1 0 1 1 1 1
  1 个评论
Stephen23
Stephen23 2023-6-15
编辑：Stephen23 2023-6-15
Ran in:
"But why does this yield the same result?"
Consider the sub-arrays (i.e. vectors) along each of the specified dimensions: what values do they have in them? Remember that all arrays implicitly have infnite trailing singleton dimensions: the fact that each of those vectors for dimensions 3 and 4 happen to have one element in them is irrelevent, ALL applies its algorithm on that one element. It might help to revise this: https://www.mathworks.com/help/matlab/math/multidimensional-arrays.html
Lets consider the top left corner of your data:
A = [0.53 0.67 0.01 0.38 0.07 0.42 0.69];
A(1,1,:) % top left, all elements along 3rd dimension
ans = 0.5300
A(1,1,1,:) % top left page1, all elements along 4th dimension
ans = 0.5300
You can repeat this yourself for every other element in your matrix.
Question: what do you expect the result to be? Why?

请先登录，再进行评论。

请先登录，再回答此问题。

回答（2 个）

the cyclist
the cyclist 2023-6-14
编辑：the cyclist 2023-6-14
Ran in:
The reason is that all MATLAB arrays have implied singleton dimension beyond the 2nd dimension, if they have not been actually specified.
A = [0.53 0.67 0.01 1.1;
0.38 0.07 0.42 0.01];
size(A,47)
ans = 1
Torsten
Torsten 2023-6-14
移动：Torsten 2023-6-14
But why does this yield the same result?
Because A has only 2 dimensions, not 3 or 4. Thus "all" operates on all elements separately in both cases.
  1 个评论
VBBV
VBBV 2023-6-15
Ran in:
Thus "all" operates on all elements separately in both cases., Yes, thats correct. But if one uses 'all' option it would do only once.
A = [0.53 0.67 0.01 1.1; 0.38 0.07 0.42 0.01]
A = 2×4
0.5300 0.6700 0.0100 1.1000 0.3800 0.0700 0.4200 0.0100
B = all(A < 0.5,'all')
B = logical
0
B = all(A < 0.5,3)
B = 2×4 logical array
0 0 1 0 1 1 1 1
B = all(A < 0.5,4)
B = 2×4 logical array
0 0 1 0 1 1 1 1

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Numerical Integration and Differential Equations 的更多信息

标签

产品


版本

R2022a

Community Treasure Hunt

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

Start Hunting!

Translated by